Pants that aren't tight at the top, so when the wearer sits down, it appears as if they have an erection.
This can lead to some pretty embarrassing experiences.
My girlfriend and I went out to lunch. I forgot not to wear to wear my boner pants, and now she thinks that she helped me achieve an erection. I'm not quite sure if this is a curse or a blessing, but at least she knows that I don't have a small penis.