For the sake of promoting Science I will tell you what all gay men know. They probably will not admit it, but they know. Observation is critical for this to work. You may need to practice.
Two things are required to make this work:
Most guys sit with their legs spread apart when relaxed. Depending on the guy, the angle between his legs could be anywhere beteen 45-90 degrees. If he is wearing boxers, or is going commando style, chances are his penis will pressed against his inner thigh. The angle of the leg is critical here. Wider angles press the penis against the leg more.
Look at the outline:
- if you see a ridge around the head, he's cut.
- If you just see a cone shape, chances are he’s uncut.
This science is not foolproof yet. YMMV. You’ll notice you can also determine other attributes .
Jockeys/Briefs are the bane of our existence.