The Guy Who's in a Squares Pool at Work
In a squares pool, everyone throws in a buck or two, and a couple people walk away with an extra 50 bucks. It's a friendly way to keep everyone involved, but there will always be one overly intense guy who shows up to your party with his own squares chart from work, where he bought a $250 square and--as he'll be certain to remind you--could win a ton of money if the Pats manage a field goal and a safety, and the Giants get a touchdown and a two-point conversion. You'll be able to spot him as the one furiously shouting, "Why the hell didn't they go for two?" when the Pats score a TD to go up 14-3.
The Football Pro Guy
Not necessarily a fan of either team, the Football Pro will spend the whole party watching the game on one of the smaller TVs on the fringe, "because I don't want to miss a play and I can't hear the announcers in that other room." He's likely to be a meatier fellow, probably will spend halftime reminiscing about high school football and will constantly use phrases like "fade hook route" and "flanker-back." He'll also let is slip at some point that he would have made it to the pros if not for an unfortunate knee injury in high school. Which may be true. Although the fact that he's 5-foot-8 with short, stubby sausage fingers probably didn't help.
Obnoxious Girl Who Cheers Way too Hard
Moderately attractive but not actually hot, she'll be decked out in full regalia of whichever team the guy she wants to sleep with likes. She'll celebrate a relatively innocuous first quarter field goal like it's just clinched the win, and will instantly show a disturbing amount of concern if a player on her adopted team is slow getting up. It'll be clear that she was molested by her father during NFL games as a child, and should be pitied, not reviled.