I guess what I list here aren't strictly faux pas, though they all do annoy me.
It should be said that I quit facebook a while back because of a combination of things such as those listed above. Yes, I am a very angry person, and stupidity online only makes me more so. I still have Twitter and MySpace though.

Here we go:
Sticking "lol" or "lmao" or "fml" or any such acronym into posts as punctuation or at the end. Only use "lol" if something is actually funny, and not if it isn't, or just mildly amusing.
Using IM/text speak in a short post. Only use it if you've got a lot to say and not many characters to say it in.
Unironic or general and liberal usage of colloquialisms and spellings. This is especially prevalant in Scotland. A little is fine, but don't go overboard.
Oh yeah, learn to spell a good chunk of common words properly. I can't understand you if you spell simple words incorrectly constantly and my general opinion of you will
Don't refer to yourself in the third person pretending you're generating a post from the website. It's irritating when you do it all the time, and highly impersonal. OK, the exception being when you're joking, but not all the fuckng time, alright?
Having lexical diarrhoea where you just post things that are neither interesting or relevant just because you can. I know Facebook and Twitter are bad for it, but you must restrain yourself.
Don't add me as a friend because you haven't seen me in a while and then never interact with me. That's just sheer narcissism on your part with regards to your friend count (hint: generally speaking, the more online "friends" you have, the less you actually have in real life).
I stopped talking to you for a fucking reason, take the hint and stop sending me friend requests.
And on the other hand, don't verbally attack me face to face if I don't reply to your request, or post you back. I was probably busy doing something more important. Like sleeping. Or breathing.
Oh yeah, while we're at it, invite me to things face to face or by phone or text or something if at all possible and not just on facebook. I can't turn up to something if I don't know about it because I stopped checking for a while.

I wouldn't have one, but if I did, it'd be called: "Fuck Off You Cunts".

I personally cannot stand "reality" TV, and I loathe and detest any participants. Mainly becuase they leave the show with absolutely zero dignity (if they ever had any in the first place) and they become these highly lauded public icons for doing nothing of any worth.
The types of show like Big Brother and I'm a Celebrity.... bore the absoulte piss out of me just for their sheer non-entertainment value. Is it entertaining to watch some brain-dead fuck sit around a house all day doing absolutely nothing? No, that's the televised equivalent of the fucking dole queue.

Spider. In My Bedroom? Eeeek! OK, calm down, man up, get off the chair. Next step?
Well, depends whether I need to use a rolled-up newspaper or a baseball bat to swat it, and whether it's big enough to steal it off me and hit me back.
If it's venomous, it can have the room, I'll find somewhere else to sleep, I don't need to get bitten fighting the fucker, and for all I know, they won't even have an antivenom for it.
It would be strange to have a large spider in my room. It's not like I live in Australia, it's too cold in Scotland for that shit.
We did nearly have a pet spider once: it ran from under the three-piece suite, going corner to corner and waiting in the dark for a while before making a break for it. It kept going round in the triangle for a couple of days, and we did contemplate putting food out for it, and sticking a leash on it while we were busy, so we could take it for walks, as it was pretty big, but we didn't.