A variety of pubitanglia
which only occurs during the time when the penis is becoming erect "extending". Sometimes referred to extendapubitanglia. Unlike repubitanglia
where pubic hair becomes entangled under the foreskin, in expubitanglia, the pubic hair becomes wrapped over or around the head of the penis and is trapped by tight fitting underwear. This condition can be avoided by regularly trimming the pubic hair.
You can tell he's got expubitanglia because of the way he walks.