I used to work with someone who constantly called semi-colons commas (and vice versa). Now, this would be irritating in the run-of-the-mill office, but we were (are!) both programmers, where commas, semi-colons, apostrophes and just about every other punctuation mark under the sun have entirely different meanings.
It all came to a head one morning where she'd repeatedly told me to put commas at the end of my lines of code. I can't remember what I ended up saying, but it was something to the effect of "Are you sure? Shouldn't it be semi-colons?" and she darn nearly ate me without salt for DARING to question her, then stormed out of the office like a petulant seven year old, leaving me sitting at my desk going "What just happened here?!"
She was a nice enough lady, but oh-so touchy...
**edited to fix a very silly typo