i hate words that are spelled the same, but that mean different things and can really fuck up the whole thing if your brain latches onto the wrong meaning.

tear as in to cry vs tear as in to rip.
live as in present tense (living) and live as in 'this is a live show'.
read as in present tense "to read a book" and read as in past tense "he read the book."
there's not a lot of them, but i especially hate them in ambiguous uses or phrases where they could mean either or.