Some of my pet peeves:
The use of "rise" and not "increase". They aren't, of course, synonyms but many people think they are.
Leaving commas out. Punctuation costs nothing.
Invented collocational phrases.
People who list something they consider substandard, and follow it up with EXACTLY the same "substandard" English usage. Missing out the subject pronoun for instance. Someone would have the vapours over the phrase "am going to the shops" yet uses "can't say I'm perfect"
People whose own small-minded ignorance makes them oblivious to regional usage. The Northern Irish usage of "bring" springs to mind.
People who use a plural noun and then write the pronoun "this". (I'm sure they'd try and defend their mistake by saying it was a typo but it just reminds one of glass houses, doesn't it?)
People who drop random capital letters into words! I mean, jeez, we learn about where a capital letter goes when we're about 4, surely? I suppose we shouldn't comment, as illiteracy IS on the rise, but it is so difficult not to smirk.
Muphry's Law is a splendid thing however. 