I've had those nights where I counted way too many drinks than I should have, and didn't feel buzzed. There are a lot of factors, like how much you've ate, how much sleep you've gotten, and even the atmosphere that will contribute. If you're sitting on your butt watching a movie at home, you don't feel it nearly as much as if it's crowded, noisy, and you're moving around a lot.
I'm a pretty little guy and I drank 2 pints of rum in about 2-3 hours once and didn't feel a thing watching a movie. The next night I went out to a club and after about 5 mixed drinks I was stumbling all over.