A little gem in my profile: "hopefully you step on one tram into overdrive son of a bitch in heat" Some guys don't seem to understand that if they play e3-f3-Kf2 chances are I'm not gonna give them a rematch.
I was cursed on Playchess after I won with 1.f3 2.Kf2 3.c3 4.Ke3 5.Kd3 6.Kc2 7.Qe1 8.Kd1.
once a player after losing in a bullet once told me that he was drunk and so couldnt concentrate
That's my excuse as I play bullet twice per day: 4:00am while still in bed on the iPad and 10:00 pm after draining a bottle or two of wine. 
There should be a thread on cocky people who start trash talking after they beat you. This is equally loathsome...maybe more.
Had a guy tell me "I'm your daddy, and am screwing your mom!" - I yelled back "dad, why must you lay with mom while you play chess with me?!"
no reply he just left lol
I got lot "you are using engines1!!" too. And then there are those who lose horribly but then win the remach and are overly cocky about that.
Still, I think the best excuse I've heard was the guy who told me that he was having a blowjob while playing.
Someone once said to me "I almost had you,but I overlooked a detail.". I replied "In other words, we had a chess game."
Doesn't sound like a sore loser. That's usually why I'm afraid of entering complications and sacrificing sometimes. It looks really good at first, blunder check, etc., but just beyond your horizon is a refutation that shores up the opponent's defense just leaving you down the exchange or a pawn in the end.
Then again it happened to Tal a lot (and sometimes the opponent even overlooks the shore up refutation!) and he was world champion.
I played three blitz games against the same person yesterday. I won the first two and he won the third one. After he said "haha, I beat you and you're using an engine". I replied "yeah, you, and 1300 rated player, just beat Rybka. I'm very impressed".