To insult stupidity:
"If life were a Mario game, your stupidity would have already cost you all your lives on the first goomba of the first level."
-- Taken from the fact that all you have to do is jump on the goomba's head. And someone who's too stupid to do that--yeah. Dead. I've used this against my older brother quite a few times.
To insult that annoying pervert that won't leave you alone:
"Not even Daryan Crescend's phallic-shaped hair would rape you."
-- I believe this requires a picture, as a non-Apollo Justice player might not get the joke without it.
To insult that sanctimonious son of a bitch you hate:
"Your head is so fucking far up your asshole that you've met The Great Mighty Poo."
-- If you've ever played Conker's Bad Fur Day, you'll get it, if not, here's the condensed version: The Great Mighty Poo is a pile of shit. No. Seriously. He even flings shit at you.
To insult a fellow gamer that seems to be aboard the HMS Failboat:
MGS-style: "Even if you took care of your box, your box wouldn't be ENOUGH to take care of you."
-- Implies that they suck. Badly.
KOF '03-style: "We're so unevenly matched that it's like taking Shingo Yabuki against Duo Lon!"
-- Shingo is the KOF character I'd vote to be "the Dan of KOF" [which means that he's so pathetically weak, he reminds me of Dan from Street Fighter]. KOF '03-version Duo Lon was too powerful for his own good--he could even beat a boss with a severe case of SNK-boss syndrome. And that's saying something. Most horrific slaughter in KOF-gaming. Bar none. Not even Shingo vs. Orochi [which I've done on an emulated version of KOF '97], Shingo vs. Adelheid [second-most horrific slaughter in KOF '03], or even Shingo vs. Magaki from KOF XI could compare. And those are pretty horrific, coming from the voice of experience.
Mortal Kombat-style: "My nephew would win. FLAWLESS VICTORY."
-- They lose. They lose without getting a HIT in. They suck so bad that even my six year old nephew who just mashes buttons would beat them without them getting a hit in.
Gungrave-style: Looks like you're about to put Grave into his namesake.
-- Lawlz. Putting Grave into a grave.
To insult that spineless wimp you hate:
"You're so spineless you're an invertebrate!"
-- This coming from a biology major. If you don't know what an invertebrate is, here's the condensed version: they lack internal skeletons, and therefore have no spinal column.
To insult your fuckwit sibling:
You: Must have been a fun crawl.
Sibling: From where?
You: From the dumpster you were dumped in when you were born.
-- Admittedly quite cruel, but I can get that way when I'm in a bad enough mood.
To insult how much someone fails at life:
"Not only have you boarded the HMS Failboat, you've already set sail and are in the middle of the Fail Sea."