A phrase used when pointing out that someone has already sunk too much effort into a situation to turn back or quit.
"I don't know if I can finish this degree, I don't even like economics..."
"dude, I know you're exhausted, but you can't quit now, you already bought the kilt."
"Why do you even want to be in his wedding if he's such a jerk? Just drop out!"
"I can't man, I have to go through with it, I already bought the kilt."
This happens when you are a male wearing athletic shorts and the draw string is tied tightly while you need to pee. Instead of attempting to undo the draw string out of laziness or frustration, you pull up one of your pant legs and underwear up and to the side so that your genitals are hanging out and you can freely pee. This is kilting.
Jake: "I had to piss really bad after gym class but I couldn't untie my shorts so I just kilted really fast in the bathroom and got out of there...I didn't even wash my hands or anything."
Josh: "you gotta do what you gotta do man"
Michael: "why is one of your buttcheeks showing while you are peeing?"
John: "I'm kilting"
Michael: "ohhhhh. gotcha."