To ejaculate into one's own pants so that the inside is creamy, but the outside is primarily clean except for what looks like some moisture. This can result from masturbating (without taking one's pants off), dry humping, or grinding, and usually results because of a case of premature ejaculation or simple carelessness.
(It's a spin-off of the term Ice Cream Paint Job)
Dude 1: God, I love grinding with Melissa.
Dude 2: I know. I got an ice cream pants job when I was grinding with her.
Dude 1: Dude! That's gross! You should go home and clean up!
Dude 2: Nah. You can't really see it. I think I'll just stay here.