Sitbomm

Acronym: Snickering In The Back Of My Mind.

!.) Typically used in text and/or chat when one finds something amusing but does not actually laugh out loud

2.) Can be used to inform a friend that their joke was short of funny, or even not funny at all.

Ralph: Did you hear the one about the sidewalk?

Sam: Um... no I guess not.

Ralph: Its all over town.

Sam (with blank expression): Sitbomm