Simply say what you haven't done ever. Next poster will then think if he/she have done that and if yes then post any happy smile what you can think of. If that person have not done that either then post any sad smile what you can think of.
Example
Player 1 : I never have shot anyone
Dexter :

Dexter: I never killed anyone
Player 1 :

And so on..
So I'll start
I never stabbed anyone