A term originated in the furry fandom. It means someone with a short penis. The word came from the thought that anthro creatures, such as wolves, have a long muzzle. If you can get past the muzzle with a blowjob, you are okay. If you can't make it (past the muzzle), you are a muzzle fucker.
"Did you hear what <asshole person> did to my car window? That Muzzle Fucker threw a rock through it!"
by Yiff-center June 20, 2018