When you are talking to either a single person or a group of people and you happen to crack a joke; that joke leads to the drive-byheckle: a total stranger happens to walk past and puts their two-cents (usually a cheesy pun) into what you just said.
Jack: ...what if in the future, making fun of someone for their age was illegal?
(Large lady in a hat walks by)
Large lady: It should be illegal NOW! (walks away)
Joe: Drive-by heckle.