Good Question! I get this same question from many of my students: What do you do when your opponent plays a strange line? The answer is simple: Following sound opening principles when making your counter-move. Beginners tend to play strange moves during the opening because they are not yet familiar with the opening principles (get central control, quickly, develop your minor pieces early and to good squares, castle your King early, don't move the same piece twice during the opening, don't bring your Queen out early, etc). It is best to continue a normal developing line that adheres to the above principles. However, you still have to be careful in regards to some of these novelty moves/lines because there is always the chance that it's a trap. It's best to play normally rather than to directly try and answer a strange move with a strange response.
Main lines vs bizarre lines
Not sure I quite buy that "follow sound opening principles" line. After all, it's fairly common that, in order to punish opening eccentricities, you have to break some rules yourself. 
The answers are better than the question. The word is "bazaar".
Karpov also lost to 1.e4 a6, and it was a regular game (although the opponent was not exactly an amateur).
Bizzarre lines are better in blitz as people have to think about them
I have a friend that plays d4 d5 Nc3 Nf6 e5 reverse scotch
Well, Reshevsky's opponent was GM Rivas Pastor, so it wasn't bad at all for ole Sammy.
GM Michele Godena must have felt terribly though when he lost following 1.Nh3 by an Italian player without FIDE title... although he lost on time in a position he had a big, probably decisive advantage.
The answers are better than the question. The word is "bazaar".
Since when does the name for a marketplace mean "very unusual"?
Sorry, melvinbluestone.
Copied from dictionary.com:
bi·zarre
1640–50; < French < Italian bizzarro lively, capricious, eccentric, first attested (circa 1300) in sense “irascible”; of disputed orig.
Related forms
ba·zaar
1590–1600; earlier bazarro < Italian ≪ Persian bāzār market
aren't all openings subjective? I'd like for you to show me where I blundered in this sequence or even where I created a weakness - otherwise you have no case.
I'd try c3, d5, or dxc before Nf3... but class players play all sorts of things OTB, they're (I'm) hardly opening theoreticians. Nf3 was fine and maybe even best if the white player was comfortable in Sicilian positions... but it would be silly to use that game as evidence of the move 1...a6 being good.
Openings aren't subjective, we're talking about chess here :p
I'm pretty sure Miles beat karpov with 1...a6
Although he tried it in a few other games vs karpov and lost hehe :)
I take umbrage!
Oh great, now we're gonna have some other poindexter running to the dictionary...
uhoh in real life:
And yet there was that ellipsis...
Oh yeah, I remember that.
Personally, I thought it was kinda funny. 
I take umbrage!
Oh great, now we're gonna have some other poindexter running to the dictionary...
I take umbrage!! And watch it with that 'poindexter' stuff, copernicus!
I was talking about the redhead kid with the OED, Tremont (if that even is your real name). And isn't it about time for you to be lassoing a triceratops for supper? Oh that's right--you moved.
I dread opening main lines. They seem like unchallenging for me to repeat over and over again. So I try bizarre stuff sometimes.
The bottom line that I think everyone will agree on is that you should stick to using sound opening principles when making your opening moves. I've had many opponents play some peculiar looking moves during the opening and these were decent chess players from a skill-set point of view. Therefore, I knew that I had to carefully examine my opponent's moves rather than dismiss them. I also knew that I had to continue with creating a solid opening plan for myself rather than directly respond to a specific bizarre move (or line for that matter). I gave a lecture about a month ago and the game I used for the lecture was Bent Larsen versus Boris Spassky. Larsen played his hallmark first move, b3 (Larsen's Opening) following by a series of moves that were not the best moves to employ against a player of Spassky's caliber. What impressed me about Spassky was his ability to develop skillfully, using a classical pawn and piece structure, no matter what Larsen threw Spassky's way. I'll stick to employing the basic opening principles no matter what my opponent is doing.
Do you play chess to be challenged or to play someone who has memorized and studied more openings? Is a game like chess more about preparation or the player who can think more creatively? Opening study is BORING. All this nonsense analysis about openings detracts from the game. And hence 960chess is superior as there isnt all this analysis.
Good evening
I am wondering how to deal with an opponent who play bizarre lines (mostly beginner player) because I never know what to do
Thank you