does-this-make-me-gay
Explanation
The Joke
A man holds up a shirt in a store and asks the clerk: "If I buy this shirt, does it make me gay?" The clerk responds: "Yes."
The clerk then explains with deadpan seriousness: "The shirt has fabric-embedded nanobots. Upon purchase, they become activated and they target the owner. They make their way to your central nervous system where they enact small structural changes to your neurons, altering your sense of sexual attraction, rendering you totally gay."
The man responds: "I don't think brain-altering nanobots exist." The clerk concludes: "Then I guess you'll still be straight."
The Humor
The comic mocks the insecurity behind the question "does this make me gay?" -- a question sometimes asked (usually about clothing, food, or activities) that reveals an anxiety about masculinity and sexual orientation. The premise that buying a particular shirt could change someone's sexual orientation is inherently absurd.
The clerk's response brilliantly highlights this absurdity by taking the question completely literally and constructing the only scenario in which the answer could actually be "yes" -- microscopic robots that physically rewire your brain. When the man rejects this fantastical explanation, the clerk's logical conclusion follows: if such technology does not exist, then no, a shirt cannot make you gay, and you will remain whatever orientation you already are.
The joke essentially forces the man to articulate out loud that his original question was nonsensical. The only way a shirt could change your sexual orientation is through science fiction technology, and since that does not exist, the question answers itself. It is a gentle but effective way of pointing out how silly the underlying anxiety is.