I love this topic. As a copy editor, bad grammar (either in writing or speaking) makes me crazy. I don't expect perfection, but if you don't have command of your native language (barring true disabilities) it's pretty sad. Regional dialects have their charm, but not knowing how to speak in professional/formal settings definitely limits your life choices.
In writing, the biggest pet peeves are not knowing when to insert an apostrophe or comma, so the individual sprinkles them throughout the sentences and they're usually wrong. Also irritating is misusing "their, they're, there," and "too, two, to."
In speaking my pet peeve is when people totally mutilate words. If there's a disability, I'm forgiving. However, if there is no excuse other than poor education/habits, I'm not so forgiving.My pet peeves:
prolly instead of probably
realator instead of realtor
lie vs. lay (you LIE on a sofa, you don't LAY on a sofa)
sit vs. set (you SIT on a sofa, you don't SET on a sofa)
And this one, which is regional (SE US): PIN used for a writing instrument. I've been in this area for 22 yrs and I still cringe at this.
Totally mangled sentences such as, "I'm going to borrie (borrow) me some sugar." My rural Georgia (US) in-laws say this all the time.
Local newspeople should know how to pronounce words, even if it's cities in other countries. Recently a local newscaster (female) pronounced Edinburgh, Scotland as "Edinburg" (as in Pittsburgh). Arghh! If she had had a question as to the pronunciation, she should have asked somebody! As it is, her report came off as unprofessional. Yes, I did contact her to correct the pronunciation.