Never show (in my opinion)
i can understand the reasoning behind showing sometimes;
say you're on the button in a tense part of a tourney, and everyone folds around to you, and you bet big
the blinds might be pissed that you could be stealing the blinds and you show your hand to them after to say " im not robbing you, I actually had a good hand "
then say later on, in the same situation you are shortstacked and its time to steal the blinds. You do so successfully, but don't show this time because you had a crappy hand. This time they know that you stole it, and will change the way they play next time.
you need to keep them guessing whether or not you really have a good hand
Like you were saying you show for humour ( AA on the BB and everyone folds to you )
but if you were not to fold, then SB and everyone else will be left guessing whether you had a hand or not
It's all about keeping them guessing...(in my opinion)
at least thats how i play