A termite walks into a bar
A termite walks into a bar and asks, "Where is the bartender?"In this joke, the humor is derived from the unstated reason for the termite asking where the bartender is. The listener is supposed to assume that the termite wants to eat the bar (or something that is wood in the bar), but thinks that the bartender will try to stop him, so he has to check to make sure that the bartender is not present, or is otherwise occupied.
Edit 12/31/19: I just realized that this is also a pun- bartender is a pun with bar tender - as in "where is the bar soft enough to be easy to eat."