Mine is one being mentioned in the other thread, so I thought I'd make a seperate one for funsies.
1. Relevant one: When a post that must've been 20 pages back is bumped up by a poster with 5 or less posts. GAH. Do people not understand how forums work? LET A DEAD THREAD STAY DEAD!
2. Any and all use of the term "red flag", especially when you're the 567th person in the thread to do it.
3. Tacky and snarky.
4. When the same answer is posted almost word for word 20 times on the first page.
Aaaand go.