Two men are pushing a bicycle with a bag on it on the curb

a policeman passes by, he thinks it’s suspicious and asks: “Hey you two, what’s in that bag?”

One says: Sand, officer!” The policeman looks. It really is sand.

“All right, you can go now, sorry for the trouble.”

A little later, when they stop two streets away, the man says to the other: See, son, that’s how you steal a bike!”