Every now and then I'll see a race televised on VS where the winning rider starts doing the happy dance before crossing the line & you can see a bit of wobble. I always wondered if someone actually went kerplunk doing that. 
Wasn't there a very high-profile pro race in which a guy thought he was the winner and started doing his victory cheer before he crossed the line but was beat at the line by the guy behind him? That was funny too.
(Sorry Flyeby, I can't drum up too much sympathy for the guy in the video since it was entirely his own doing.)
2009 Lynskey R230 Houseblend - Brooks Team Pro
2007 Rivendell Bleriot - Rivet Pearl