ilshimimp

Acronym - I'm laugh-ing(-ed) so hard I messed in my pants.
Origin unknown, but most likely created within and due to the internet.

This acronym can be used in the past and present participle, unlike most that can refer to only one occasion.

Subject One: That is funny. Hahaha.
Subject Two: I concur.
Subject One: Oh dear.
Subject Two: What is the matter?
Subject One: ILSHIMIMP.
Subject Two: Oh dear. I shall fetch you some fresh undergarments.