Debagging

Debagging, also known as "depantsing" or just "pantsing" in the US, is the pulling down of a person's trousers and/or underwear mostly against their wishes, typically as a practical joke, but in other instances as a (somewhat common) sexual fetish. The most common method is to sneak up behind the intended victim, grab the trousers at the waist, and apply a quick downward tug before the victim is aware of the assailant's presence.