When your sitting in a quite area and you can tell someone in the other room told a really good joke because you can hear them laughing so hard they start pounding on the table.
Tom: "Hey man did you find the answer to numbe......"
People in other room: "ah ha ha ha no fuckin' way ha ha ha ha ha hAAAAA!!!"
Daniel: "Wow those fuckers are really yucking it up in there aren't they"
Tom: "Yeah someone must of told a real knee slapper in there." "Good enough to keep us from working."
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"