One thing that turns me off is when people (wrongly) use 'alphabet' in place of 'letter'. An alphabet is a collection of letters. 'A', 'b', 'c' are letters. They are not alphabets. Everytime I hear someone say it wrong, I'm tempted to correct them whether they like it or not, and I often do.

Don't make that (painful, painful) gaffe. At least don't make it in front of me.