Slap

From LittleBigPlanet Wiki

A Slap is when a Sackperson moves it's arm around, making it Slap another Sackperson. To Slap another Sackperson, swing your left (L2 + Left Stick) or your right (R2 + Right Stick) arm (depending on where your target is) quickly away from you by flicking the stick. It also works to quickly rotate one of the Sticks. When a successful Slap is made, the Sackperson smacks the nearest player and shakes it's hand to relieve the pain from the Slap they made. The Sack that got Slapped however, will twist and fall, but then get up okay. Unless, of course, they are knocked onto something dangerous such as spikes or electricity; a great way to deal with an annoying player or someone who's got all the points. It's common for Slaps to occur when players gather at a Scoreboard; the winner usually takes the most of it.

Also, when slapping with the accessory, Frying Pan, in hand it makes a clang noise instead of the normal slap noise.