Slang doesn't bother me.
Grammar does.
Some of the most ridiculous Americanisms I see these days;
- Could care less (though it is stopping now.)
- Off of (incorrect 100% of the time, and used in place of 'from' or 'on' or simply incorrectly adding 'of' where it is unnecessary. I.e. "I took the salt off the table" = correct. "I took the salt off of the table" = moron. Absolutely taking off at the moment, so obviously a result of a lack of education funding.
- Couple things / couple whatever etc. The correct form is 'couple of x' never 'couple x'
- For speech; Data. Really it isn't that difficult, it's day-tah, not 'dah-tah'. This is a particularly annoying one for me as in video games with voice acting you'll often get two different NPCs saying the word differently, and no one bothers to correct it.