Do you mean swimsuit bikini bottoms or panties, such as so called "bikini bottom" underwear, under lowrise pants, with your ass hanging out? If swimsuit, string? Either way, does half your ass hanging out mean half your ass crack visible or just a lot of upper ass flesh flashing, without much crack sighted?
Today going commando and currently on the computer shirtless with the fly on my jeans open. Really enjoying the sensation of the soft, loose denim shifting around when I move my legs, lightly brushing my upper ass cheeks and softly caressing a warm erection gently nestled between my thigh and the jeans' upper left pant leg near the crotch. Ohhhhhh yeahhhh...