This may be kind of arbitrary or unusually specific, but one of my big pet peeve's is the misuse of apostrophe's. Especially in sentence's when people are trying to make single nouns into plural's when they actually are making them into posessive's.
For all those who don't know what I mean, then check out this webpage which claims to be from the
'apostrophe protection society.'. And for something slightly more credible-looking,
this webpage is from Purdue University's website.
And yes, that first paragraph was an example of poor apostrophe usage.