1) What you're probably doing right now if you're on this site reading definitions instead of doing your damn homework, and not supposed to be on the computer. Usually accompanied by snorts and gasps, as well as tearing of the eyes and spasms.
2) What you do when your friend's brother disses your friend real good, and you don't want your friend to get pissed at you for laughing your ass off.
Son: "*buckling with silent laughter* Sh-hart! Ha ha ha ha...!"
2) Brother: "Go give Kevin's sis a hot Carl, you fucking SP.ED."
You: "Hee..Hee...*silent laughing*"
Friend: "What the fuck are you laughing for, get the hell out of my house!"