I have 2 pet peeves that come to mind.

1)The wave of amnesia that is sweeping society regarding the use of the apostrophe for possesives, NOT plurals. (ie: The club will meet on Sunday's from now on.) I even see it in newspapers and magazines now.

2)This is not a language peeve per se, but I HATE when people spend time on my voice mail guessing where I might be. "Maybe you're working in the garden, maybe you're writing, maybe you're out doing errands or working late at the rehab" Ay yi yi, just leave the message!