If people do that against me I usually mutter a little 'patience young Padawan' to myself, then move along to my next game without even looking at their move. They can wait until I'm ready to make my next move just like everyone else.
Haha, I like to do it in openings and end games or moves that I know 100% I will play
Like Tonya H. said in post #15 conditional moves existed before the internet.
If it was 1980 and you were playing by snail mail and you got a postcard that included conditional moves, would you be insulted? Just opening it up for discussion.
(The difference, apparently, that you could see it on your postcard, while on this system it happens immediately after you make your move.)
YEAH
Is it cheating to pre-move using a Palantir?
The Palantirs are not all accounted for. We do not know who else may be pre-moving.
OMG
An interesting variety of responses. I tend to have 10-15 daily games on the go at any one time, but don't have masses of free time to devote to chess. So, when against someone who I know is likely to reply immediately, I tend not to respond quickly even if the next move is totally obvious, in order to buy time to focus on games where the next move requires a bit more thought.
I get the point about using pre-moves against someone who's petulantly playing on in a totally lost position, but thankfully none of my opponents in daily chess have ever done this to me. I've experienced it loads of times in live chess though, and been guilty of it myself tbh 
As for replying straight away...I mainly play on my phone which vibrates when the move comes in; I enjoy my games, they are not idle curiosities; I calculate so have normally considered a few of my opponents replies and my responses based on the position and a plan. Based on all that, if the phone goes off and I'm not doing anything that cant be put down for a few moments, and their move is one I anticipated (and maybe was relishing), why not knock out the reply? You recognise that your feelings are irrational which is good. Try to be more tolerant of differences. These things aren't good, bad, right or wrong. They are just different to your preferences.
BTW you may also be overlooking that much of the chess world has a great deal of free time at the moment. The UK is in another national lockdown until the middle of February for example, I'm only supposed to leave my house for work, exercise and essential shopping. Leaves a great deal of time for chess. It's not easy to 'Get a Life' at the moment.
A lot depends on the scenario. There is absolutely nothing wrong with conditional moves in correspondence chess. Now, I do not go around guessing moves every move. Totally stupid. But I will use it in the following conditions:
1) Forcing sequences - This does not mean the only legal move, but let's say I am White, and it is a long series of captures where there is no intermezzio for Black at any point, and all moves except recapture lose. I will put in conditional moves.
2) Only 1 moves is legal, like Qxf7+ (protected by another piece, nothing hits f7 by Black except the King on g8 with Black pawns on g7 and h7), and Black's only legal move is Kh8.
3) Ridiculous positions where the opponent is just being a jerk about it and will not resign. Correspondence is not blitz or bullet. I almost never resign in blitz or bullet, but rapid or correspondence? Absolutely! What do I mean by ridiculous? I am up so much material, like say the following with no comp for Black. I will put in conditionals of all common moves for Black. For now they would be 2-movers, and ad his choices diminish, the conditional lines would get deeper. Black should simply resign. There is no reason to play on in this. Blitz or bullet? Sure! Not Correspondence!
The reason I never do pre_move, is that, the first time I've read about Correspondence Chess and conditional moves, it had that little story in it, that traumatized me:
A player played 1.e4. His opponent replied boldly: "1...-b6 and on "any" 2...-Bb7". The first player went "Okay, 2.Ba6-Bb7 3.Bxb7"
Oh ya . This was one of the bizarre incidents. But you realize here there is no option that lets you select a move for "for any" ..... You can chose the lines.
“The purpose of this post is not to complain.” - OP
Nonsense! That is exactly the purpose as you admit to becoming irrationally put- off.
Nothing to become upset about .... small potatoes.
The original intent was to save a postage stamp.
I don't understand all the hostility. It doesn't give me any kind of pleasure to imagine I've irritated my opponent, and it saddens me to hear how testy people can be. Some people get annoyed if you take longer to move than necessary. Some people get annoyed if you move too quickly. Good gamesmanship isn't just about abiding by a code of conduct. It's also about having the generosity of spirit to tolerate an opponents foibles and keep a friendly attitude.
Like Tonya H. said in post #15 conditional moves existed before the internet.
If it was 1980 and you were playing by snail mail and you got a postcard that included conditional moves, would you be insulted? Just opening it up for discussion.
(The difference, apparently, that you could see it on your postcard, while on this system it happens immediately after you make your move.)
I'm old enough to have played correspondence chess using paper post cards in the regular mail. We routinely used conditional moves since theses games took years to finish. I was happy to see conditionals from my opponents (and even thought I should use conditionals too, out of respect for my opponent). I won one of my snail-mail CC games when my opponent died of old age -- the ultimate "win on time" (okay to joke about it now since that was 40 years ago!).
OMG YOU WILL PLAY CHESS WITH PAPER POST CARDS
“The purpose of this post is not to complain.” - OP
Nonsense! That is exactly the purpose as you admit to becoming irrationally put- off.
Nothing to become upset about .... small potatoes.
The original intent was to save a postage stamp.
No. The purpose of the post was to enquire as to whether others share my reaction (rational or otherwise) of feeling slightly irked by such behaviour.
It would be an exaggeration to say I get 'upset' over opponents doing this. It's mild irritation at best.
Small potatoes yes, but it's arguably even more petty to go to the trouble of insisting I'm having a moan when the original post a) clearly poses a question, and b) states unambiguously that my opponents have in no way done anything wrong.
Okay I understand
As for replying straight away...I mainly play on my phone which vibrates when the move comes in; I enjoy my games, they are not idle curiosities; I calculate so have normally considered a few of my opponents replies and my responses based on the position and a plan. Based on all that, if the phone goes off and I'm not doing anything that cant be put down for a few moments, and their move is one I anticipated (and maybe was relishing), why not knock out the reply? You recognise that your feelings are irrational which is good. Try to be more tolerant of differences. These things aren't good, bad, right or wrong. They are just different to your preferences.
Fair enough.
Okay I understand
Awesome. I can rest easy now.
There are only 2 realistic scenarios here:
1. The next move is obvious to both parties, like a recapture of a multi-move exchange of pieces in progress, for example...in which you have no cause for complaint.
2. The move was obvious enough to set a conditional move (it's not actually a pre-move), but only to your opponent, and it took you a while to arrive at the same conclusion. In which case you are just embarrassed that he/she is way ahead of you, and have no cause for complaint.
Summary: no cause for complaint.
If we are playing and you hang your queen, would you like me to ponder for 3-5 minutes before taking it so you can feel better? You won't feel better , it will feel worse the longer you sit there waiting for the inevitable...that's because you are the cause of your own irritation, not your opponent.
Or, just do speculative sacrifices all the time...nobody will set any conditionals on those. You'll lose more often than you win, but at least you'll be unpredictable.
Sure if you have to defeat the armies of Mordor in order to get a Chess set carved in Orc's bones so you can play with an Ent, it's maybe a better idea to switch to Golf. With metal clubs. And plastic balls. Then wait for someone to invent plastic.
One does not simply pre-move in Mordor.