Boys vs. Girls: Arithmetic

overheard at a restaurant...
boy: "I think I should drive tonight, you had too much to drink."
girl: "No... I should drive... you drank more than me!"
boy: "I had 1 drink."
girl: "I also had 1 drink."
boy: "My cooler was only 7% alcohol. Your wine was 14% alcohol."
girl: "No... the whole bottle is 14%. I just had 1 glass."
(pause)
boy: "I am definitely driving."