When you light the paper of a joint such that there's a small amount of weed hanging over, you have a cumtail.
Better weed packing and better lighting techniques can prevent the formation of cumtails, but they are also just smokable that way (e.g. by ash wizards)
"Aw dude I got a huge cumtail this joint is ruined"
"are you fucking stupid?"
"you can't be smarter than everyone"
"wanna watch me piss?"