Ted's hypothetical scenario is one where one party takes advantage of another party's drunkenness by repeatedly requesting sex until the other party gives in. He then asks what happens if both parties are equally drunk. The answer's pretty straightforward - the one repeatedly requesting sex clearly wanted sex, and so it's ridiculous to claim that they were unaware of what they were doing. For it to be symmetrical, both parties would need to be asking the other party for sex even though they didn't want it themselves. That's absurd. The situation isn't symmetrical, and Ted's defence doesn't rely on symmetry.