I can forgive some grammar mistakes, for example I have no issue with ending sentances with prepositions in conversation. It has become so commonplace we might as well rewrite the rules regarding that.

Also using "their" as a singular pronoun referencing anything belonging to a person of unknown gender is pretty universal now. "His or her" just doesn't flow nicely.

The ones that get me the most are single words. Irregardless, flammable, misunderestimated... lol

My biggest pet peeve though is people who say they want to "go to Chipolte for lunch". It's not "Chipolte". It's "Chipotle". I realize it isn't an english-specific word, but come on. I can understand difficulty with pronouncing certain vowels or consonants that are slightly different than our own, but re-arranging the order of the letters in a word?

That's only forgivable if you are 4 years old or lysdexic.