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.
An English translation could be
The video is so funny you'll pee your pants.
I just peed myself – it's so funny.
Both German and English phrases are obviously colloquial and vulgar expressions.
I would translate this with
to be convulsed with laughter.
It probably comes from wetting your pants while laughing so hard, as
pissen means to piss.
I would translate it as "piss away."
That could have a literal connotation of "urination." But it might also mean "to waste," as to "piss away" (waste) time.
In this regard, the German synonym I might use is "wegwerfen."