It's impossible to talk about "gay for it" without talking about humor. The phrase is almost always delivered with a wink. It's a joke, but it's a joke that carries real meaning. This ironic distance is crucial. It allows people to say something potentially vulnerable or controversial in a way that feels safe.
Consider the classic example: a straight guy at a party sees a famously attractive actor on screen. He turns to his friend and says, "Okay, I'd be gay for him." The friend laughs. They both know it's a joke. But they also both know there's a kernel of truth in it. The humor defuses the tension. It creates a space where a straight man can admit to finding another man attractive without facing social consequences.
This ironic framing is a hallmark of modern internet culture. It's the same mechanism that drives memes, shitposting, and self-deprecating humor. It allows for honesty under the cover of comedy.