Diagonal? Down the middle? Halves or quarters?
Me, I don't give a shit, especially if someone else has made it for me. If I make it, I just cut it down the middle because it tastes the same no matter what and takes less focus than trying to get a line from corner to corner. Heck, it's going to be ingested within five minutes, anyway.
Believe it or not, there are some really uptight folks on this issue. I ain't one of 'em.