when someone laughs so hard that they fart .

Luser Attitude Readjustment Tool

1. n. In the collective mythos of scary devil monastery, this is an essential item in the toolkit of every BOFH. The LART classic is a 2x4 or other large billet of wood usable as a club, to be applied upside the head of spammers and other people who cause sysadmins more grief than just naturally goes with the job. Perennial debates rage on alt.sysadmin.recovery over what constitutes the truly effective LART; knobkerries, semiautomatic weapons, flamethrowers, and tactical nukes all have their partisans. Compare clue-by-four.
2. v. To use a LART. Some would add "in malice", but some sysadmins do prefer to gently lart their users as a first (and sometimes final) warning.
3. interj. Calling for one's LART, much as a surgeon might call "Scalpel!".
4. interj. rare Used in flames as a rebuke. "LART! LART! LART!"

Larting is when you laugh so hard you fart

Adjective:
1 doing something or taking place after someone has shat themselves
2 belonging or taking place near the end of shat.
Adverb:
1 After the shat
2 toward the end of a shat

the act of laughing so hard that one farts.

The accidental Fart released during laughing really hard.

To laugh and fart at the same time, at a joke that isn’t funny, then follow it with more laughing.