Gary WAS f***ing with all of the other housemates, but he was such a lone wolf, it was hilarious. Also a good deal of it was based on real impairments he had--he just emphasized it even more, and because they were all such toads last series, we loved seeing them get one pulled over on them. He had a huge ego, but he's a good enough actor, even still, to sublimate that to getting the others in trouble. He was sneaky... in an interesting way.
Perez is more like a mean girl than a lone wolf. It's not funny when it comes from him, because it's petty, it's ultimately seriously about boosting his own ego. There's no subtlety to it, and while there's the rare moment of brilliance (like him fake-orgasming when the girls were all so viciously fighting) , they're few and far between, and like that moment usually based from a pretty dark place. Gary liked getting one over on the rest, with a smile, but Perez likes hurting people--but then lying and fake crying about how he doesn't want anyone to think he's a bad person... news flash Perez... you're a bad person. Seriously.