1)when someone is doing something they shouldn't be doing or when what they are doing is annoying
2)what someone was doing when they were supposed to be hanging with you
² A great way to get a buzz/adrenaline rush for all those involved
³ A cheap excuse to cop a feel.
Did you see that topless chick get tickled on the Howard Stern Show? That was hawt!
Tickling - If you can't watch porn, there's always tickling!
Sam: "what are you doing.."
Joe: "This is called tickling the lock"