I play a lot of 2 1 on live chess (I can't play anything quicker, but I like to play quick :D), and a few times my opponents have complained about the bonus time. It has happened when I was dominating in the endgame, but with very little time left. Naturally I could survive with the extra second, and with the premoves easily rack up time. 

Now a few times my opponents have called this bullshit and I don't understand why. They accepted my challenge, they should be aware of this. Has this happened to any of you guys before, and what is your opinion on this?

I think you should have an increment. Just because of the nature of chess games can vary in length greatly. Timed games are supposed to be about managing time (in my humble opinion), not just seeing who can move their hand over to the clock the quickest.

I prefer using increments myself. It avoids the mindless mouse racing that often occurs in their absence. With an increment of five seconds or so, moves might actually have consequences. It's not your fault if your opponents don't understand them and use the same strategies trying to win on time.

Increments were what I was talking about (on live chess it's labeled bonus time)

If someone doesnt like playing with an increment, they shouldnt sign up to play that kind of game. The system is pretty clear about when there is an increment and when there is not. Just my $0.02

Well, I don't care but if I understand you well, you just make any possible move as quick as possible to gain some time from increments? If so, then I can understand your opponents (for example Q an K vs. K endgame with 1 second for you and thirty for your opponent - and you move your queen around to get more seconds). If they complain only because of the thing, that your time is not over and you play to win not to get time, then it is unreasonable behavior. That's for me