humiliating
Explanation
The Joke
A woman confesses to a man named Ted that she only slept with him because she has a fetish for humiliation. Ted is confused and replies, "But we didn't do anything humiliating." The woman responds: "Well... you didn't." This implies that she finds the act of sleeping with Ted to be inherently humiliating for her -- a devastating insult to Ted's sexual desirability.
Ted is shown blushing and looking mortified as the implication sinks in. The woman then says "Wow, that is hot!" because Ted's visible humiliation and embarrassment is exactly what feeds her fetish. Ted responds with an exasperated "SEE!?" -- presumably confirming that this is exactly the kind of humiliating loop he has been trapped in.
The Humor
The comic constructs a perfect logical trap. The woman's humiliation fetish creates a paradox: by telling Ted that sleeping with him was humiliating, she humiliates him, which she finds arousing. His reaction of embarrassment only makes it worse (or better, from her perspective). Every layer of his discomfort validates her original statement. He cannot escape: if he is upset, she is turned on by his humiliation; if he is not upset, then presumably the original insult stands unchallenged.
The humor also comes from the brutal, almost casual cruelty of the insult buried within the confession. What initially sounds like a vulnerable moment of honesty ("I have a fetish") quickly becomes a devastating burn ("sleeping with you was, by itself, humiliating enough to satisfy that fetish"). The final panel's "SEE!?" suggests Ted has tried to explain this impossible situation to someone before and has not been believed.