Someone who acts dumber then they are. A moron, an idiot, generally derogatory.
Often used to convey frustration when dealing with a person that has intellectually regressed to a caveman.
Tim: Barry, I have something important to tell you, please pay attention
Barry: Wait, check this out - I think I can navigate my iphone with my nipple!
Tim: Truly extraordinary. You know what? ... You can be a real schmuck sometimes.
A marlin is a hot ass chick -- similar to pulling in a massive fish against all odds. Pictures are usually taken with the marlin (to share on Facebook later). A mullet is the opposite -- similar to reeling in a line and wondering how that fish ate your bait.
Daddy: "Dude! Did you see that girl I was talking to at the bar?! Marlin status."
Murray: "Marlin? Um...more like mullet. Total marlin vs. mullet confusion. I took a photo of you guys and put it on Facebook. I tagged it #thewrongkindofbigfish."