About fifth base when there's really only four bases reminds me of the expression uptoeleven.
What is first base in dating
A walk is considered a sympathy base and is typically reserved for first base only.
What is first base in dating terms
Don't use "hit" with "bases," but you can use the baseball terms that correspond to hits:I hit a triple when i took her home last night.
Of the other answers has provided a nice link to the wikipedia entry for baseball metaphors for sex.
" "i didn't think i had a chance, but i made it to third base with her last night.
Didn't think i had a chance, but i made it to third base with her last night.