I find getting excuses in early seems to be popular and a somewhat effective tip! (See most pages of this thread for inspiration!)
The obvious classics are injuries both short term and longstanding. And family and work selfishly getting in the way of your professional training program. If this is followed by a barnstorming performance it is even more effective! (One that springs to mind is Bobinski, suggesting he was taking time out as his knee was about to drop off, then putting in monster performances to blow everyone else away!


)
Post race is a time for sulking and weazing in equal order. You may want to give some begrudging kudos to the victor or you may find yourself genuinely enthused by the performance of yourself and others. It is actually quite satisfying seeing other people do well but if I'm frustrated I have the choice of 3 cats to kick!
If you don't have a pet cat I'm sure any animal or small child will do (maybe not a bear though randy...)
Somewhat insincere apologies for challenging and beating other people's ghosts are also both effective and awesome needle at this point! "Oh dear, sorry about that, heh heh heh" etc etc....
These probably weren't the tips you were after to be fair... So I should add that after a race I like a peanut butter sandwich and a Choco milk. Both recommended to improve recovery etc and also well deserved and delicious!
But most importantly, brush yourself off, and come back next time for more of the same.