This old but one of my favorites:
An old cowboy sat down at the bar and ordered a drink. As he sat sipping his drink, a young woman sat down next to him. She turned to the cowboy and asked, "Are you a real cowboy?"
He replied, "Well, I've spent my whole life, breaking colts, working cows, going to rodeos, fixing fences, pulling calves, bailing hay, doctoring calves, cleaning my barn, fixing flats, working on tractors, and feeding my dogs, so I guess I am a cowboy."
She said, "I'm a lesbian. I spend my whole day thinking about women. As soon as I get up in the morning, I think about women. When I shower, I think about women. When I watch TV, I think about women. I even think about women when I eat. It seems that everything makes me think of women."
The two sat sipping in silence.
A little while later, a man sat down on the other side of the old cowboy and asked, "Are you a real cowboy?"
He replied, "I always thought I was, but I just found out I'm a lesbian."