1. the sixth letter of the alphabet, pronounced "eff"
2. A very very very very very bad grade, which usually prompts disciplinary actions by parents of young children.
3. the last letter in the slang acronym WTF, which is commonly used often by n00bs, or used occasionally by l33ts to indicate surprise, shock, or rejection towards something.
1. F is a letter, use it.
2. I got an F on my Physics test, looks like father is going to tie me to that tree in the front yard and flog me until i'm sunburn red.