My favorites:
Saying "ironic" when "coincidental" is intended. Ironic means the outcome is the opposite of what was expected. Coincidence means there is a seemingly inexplicable correlation. Special thanks to Alanis Morrissette for fucking this up for all of us.
Saying an acronym, followed by the last word in the acronym, like "HIV virus" or "ATM machine".
"Often times." Doesn't "often" mean "many times"?
"For all intensive purposes." What is an intensive purpose? It is supposed to be "for all intents and purposes".
People who talk about the hardness of "a cement slab." I think they mean concrete, since cement is the gray powdery stuff that comes in a 50 pound bag.
"Pre-planned," "pre-existing," "pre-"anything. How do you pre-plan something? Plan it before it is planned? If you plan it before you execute it, then it is planned, that's all there is to it. Same with a “pre-existing condition”…if it already existed, then it is an "existing condition."
The"grammar Nazi"Rover