One of the earliest off color jokes I ever heard:

A naked girl is hitchhiking on a rural road and a guy comes along on a bicycle. She says, "Please give me a lift!? He answers, "Sure! Just climb up here on the crossbar." They go on down the road and he doesn't seem to notice that she's naked. After a while she say, "Good sir, if you haven't noticed, I must tell you that I am naked!" And he answers, "And you haven't noticed that this is a girl's bike!!!"

Art