you somehow decide its a good idea while inebriated to hide in your mate's closet and leap out to give him a scare, only to have him and his bird come in and getting it on before you quite realise what was happening.
and then of course, deciding to tough it out even though you desperately need to take a piss, to save everyone the embarrassment...
before giving up and falling out halfway through their exertions, and just legging it to the bathroom during the shocked silence.