Diaper ? I dont find that funny at all. If you just pissed your panties then i'd find that funny... and a little bit, just a bit of eww at the same time. As someone else suggested, using a bottle would be a funny too.
I guess there might be people who are into shy girl in mech who wont come out to go to school and wears diapers. But not for me. I found it boring.