A construction worker on the 5th floor of a building needed a handsaw. So he spots another worker on the ground floor and yells down to him, but he can't hear him. So the worker on the 5th floor tries sign language.
He pointed to his eye meaning "I", pointed to his knee meaning "need", then moved his hand back and forth in a hand saw motion. The man on the ground floor nods his head, pulls down his pants, whips out his cock and starts masturbating.
The worker on 5th floor gets so pissed off he runs down to the ground floor and says, "What the fuck is your problem!!! I said I needed a hand saw!".
The other guy says, "I knew that! I was just trying to tell you I'm coming!"(source)