Can't believe I haven't posted in this ever.
Anyway. Gary.
One of the most overrated characters I've ever come across (which is saying something) and even two years of absence haven't changed my opinion on this in the slightest.
Still, seeing as he isn't even in 95% of the game and doesn't appear outside of story segments he can be hardly listed as a 'worst' enemy.
Yet again, Damon has to be my nemesis and there's nothing quite like beating him up whenever I walk almost anywhere, especially if I stick at the end of chapter 4 like I used to. He's also noteworthy because he spawns very commonly unlike Bif who is stronger and Russell who never engages you outside of chapter 1 unless you engage him first. I'm also pretty sure Russell doesn't spawn outside of Halloween in chapter 1 but I could be mistaken.
Either way, he never engages on you after chapter 1 whereas Damon will probably attack you from the start until the end of chapter 4 briefly stopping then attacking you until the end of the game.
Funny thing about Bif though, was doing Beach Rumble and afterwards Ricky was available for hire. Love working with Ricky, every time that bit comes up I think the game could have gone a different direction where you make friends within a faction even if your status with the faction itself is mediocre keeping the faction rating much more dynamic, but alas, not to be. In any case, hired Ricky and came across Bif, and Justin who engaged me and Ricky on sight, fine by me. However as I tried to taunt Bif, he was focused on Ricky, so I was constantly giving him wedgies and Ricky was beating the crap out of him.