I debated with myself about whether or not to post this for a while. I can guess what will happen is that the transphobic assholes will crawl in and shit on it, but I think it serves as a valuable example of what not to say if you don't want to be perceived as an asshole. From this thread:
Please don't use "coopt" about other people's identities/bodies/desires. I see this a lot from two groups: 1. angry feminists who hate men and trans people and 2. gay men who get bent out of shape about people allegedly stealing their fabulousness. Both groups suck, in a non-fun way. If somebody identifies with having a penis, it is not your place to question that.
Yeah, there are women out there who read M/M porn and really objectify gay men. It was done to lesbians for a long ass time and is still going on. (But, oh, they're women. They're used to being objectified and we can just laugh it off when they complain.) There are also female-assigned-at-birth people who identify as men or identify with aspects of masculinity. The cis-privilege I see every time the word "coopt" come up in regards to those people (MY people) makes me sick.
Also, please don't call somebody a lesbian who doesn't identify as such. By lumping different identities together, you are insulting lesbians, bisexuals and genderqueers right there. Doubly offensive in this case is that you're making assumptions about the gender of hir partner as well.
The general rule is you don't go mocking somebody else's identity unless you know 100% that they are cool with it or else they started it. Those of us who can be visually identified as "other" are particularly sensitive about this sort of thing. Just because your trans, or black, or disabled friends don't tell you off doesn't necessarily mean they think it's funny. And just because ONE of your friends is okay with it doesn't mean everybody is. Don't assume because one time you screwed a black guy and he liked being called Sambo while you spanked him means you can make racist jokes now.
It's like being stuck in an elevator with somebody who's farting. Sometimes it's easier just to stay quiet and get out as fast as you can. Unfortunately, there are people who think "hurr hurr, nobody hit me, I funny!"
Consider this that gentle (loving, even!) bap on the nose. Don't fart in the elevator.