After some years in the professional world with people who claim that they are fluent in English, here are the top irritants that I encounter at work (and yes, even from the managers):
1) As per
Instead of using: according to, as stated in, in accordance with
Example: As per your request (As you requested)
Nobody uses this in casual conversation nowadays!
Instead of using: regardless, irrespective
Ir + less = double negation. Self-explanatory