These are the grammatical mistakes that REALLY bug me.
1. less/fewer – gets top billing because of how common it is. Drives me crazy every time.
2. using “enjoy” as an intransitive verb. I cannot simply enjoy, I must enjoy my dinner, my food, my evening, my grammar dalek habits.
3. using an apostrophe to indicate a plural. There have been angry review notes about this one on my audit files. Worse when the rule about words ending in s followed by an apostrophe is correctly used while making a mistake (e.g. There were two thesaurus’).
7. refusing to acknowledge that “data” is a plural noun and therefore claiming that “these data” is wrong. I’ll accept “this data” as common usage, but don’t tell me the plural is wrong.
8. amount/number. Amount of cheese, number of cheeses. It’s really not that hard.
Any travesties I’ve missed?