Refers to the condition of a man's testicles 5 days or so after shaving them. Round and prickly, the Pant Cactus is a foe to one's comfort, inner thighs, and the ladies. See: Manscape
"I look like a perv because I have to keep adjusting my balls - this Pant Cactus is so damn prickly! I'm never shaving my balls again!"