Well, theres this one guy I play a lot (unfortunately) and whenever he's about to lose he declares he'd got bored and given up about 20 moves ago... talk about bad loser! But I digress.
I've had someone say that they lost because of their broken arm... And we weren't even using a clock, so...
That's odd, I remembered that anecdote as coming from one of the Polgar girls, who remarked "I never beat a well man" after the old club players her dad brought her to crush would always make excuses.
Nimzovicth screaming and thrown a pieces:- "How I can loose to such an Idiot"?
Gufeld grab a bunch of Knights,and trown them into the board of one of his famous students, after the loss of that player, by putting twice one Knight and another Knight on the same wrong square, and loss both Knights, and the Game!
'Are you need even more Knights!???"- asked Gufeld...
After loosing his Match, Tal explain: "Now I am not a Tal! I am a half-Tal!"
Referring for his partner Polygaevsky ...
"Poly" - means "Half" in Russian Language!
It's a good idea to set up an alibi ahead of time. For example, when I sit down with my OTB friend, I might tell him that I feel like crap because i drank too much and didn't get enough sleep last night. That way, if he wins, the alibi is already in place, but if he loses, then he's been beaten by a sick old man. 
just coaching u. i took obvious unnecessary risks, to see how u handle it.
'I never beat the healthy opponent!'-
Fisher said it, after beaten M.E. Taimanov, who complained, that he got a hypertension...
What you know about all kind of real 'chess excuses' to loss?
What you read from other sources?
It can be a very funny, tragic, awesome!