Sometimes I read the following expressions:
Dieses Video ist zum Wegpissen.
Ich könnt mich jedesmal wegpissen!
Obviously "to piss off" does not fit the context. Where does this expression come from, and how would it be translated?
sich wegpissen has probably evolved from
Sich wegschmeißen vor lachen
(which is not vulgar) and
Sich bepissen vor lachen.
As has already been said by others, the latter one obviously comes from the imagination that you have to lough so hard you can't hold back your urine anymore. Like in your example you can say
Dieses Video ist zum Wegschmeißen.
Which is a quite common expression and will be understood without mentioning the verb
lachen. I think this is when the two expressions above have been mixed up to
According to Google, the expression
zum Bepissen is much more common than
zum Wegpissen (425,000 vs 15,400) which leads me to the conclusion that it has arisen as assumed above.