My favourite example of this is Hab SoSlI' Quch in Klingon, which means your mother has a smooth forehead. Of course, Klingon is a made-up language from Star Trek, but, they had to figure it out as they went along. I don't think there was a formal Klingon language in the 1960s when the race was introduced. The language became official and learnable in the 1990s or 2000s. And "your mother has a smooth forehead" most likely comes from Worf's son Alexander, whose mother is human. So Klingons are like 3-5x stronger than humans, and this definitely includes the females. Star Trek VII established that backhanding a Klingon woman was part of a mating ritual (this was sort of played for laughs, but also, a man hitting a woman is never really funny), so the idea was, a Klingon man is not a real man if he has a human woman for a mate, because it means he can't handle a Klingon woman. Now, a lot of races have weird rules about dating outside your race, and it's disgusting. Star Trek was playing to that. There's nothing fundamentally wrong with a Klingon man finding love with a human woman (and IIRC we never met her, but Worf would go on to get married to a Trill named Jadzia Dax on Deep Space Nine, and while Trills are interesting, they're no stronger than humans, so similar point). But Klingons are all about honour, so when someone told Alexander "your mother has a smooth forehead," they were saying his father lacked the honour to mate with a true Klingon woman, and that dishonour was hereditary.

I like Japanese cursing. The ones I know aren't about what you are, it's about what you lack. Baka is everyone's first Japanese word, it seems like, and it means idiot, but it's more like... "one who lacks sense." They're shaming you for doing dumb shit. Or "hentai," which means pervert (it also means porn, but, like, the kinky shit, but it really means someone who would watch that), but it's more like "one who lacks tact." The less common one, "aho" is exactly what you think if you know English curses. Often translating to "jerk," it's literally just "asshole" with fewer letters, and means the exact same thing. Except it's more like "you lack kindness." It's the difference between flipping someone off when they cut you off in traffic (cursing in English) vs giving them a thumbs-down (cursing in Japanese). One makes them hostile toward you while the other gives them more of a chance to reflect on what they did. And maybe that's the point.

I wanna know if you can curse in Loxian, but only two people know it, and they're two of the most gentle souls on the planet, and one of them made the language, so I highly doubt you can curse in Loxian. Loxian was made by Roma Ryan, and the only other speaker of the language is the Irish singer, Enya — who Ryan writes songs for and has done for 40 years. This is what it sounds like. Yes, it sounds like Gaelic — it's meant to. They actually came up with a whole back story for the language. The Loxians are just Irish people in the future who traveled to the stars, first by way of Mars, then through the Loxian gate (which I guess is like a Stargate in space, like Stargate Universe had?) to travel to a faraway galaxy. So it's like future Gaelic/Irish. And she has four other songs in Loxian. Yeah, probably no swearing in Loxian... I mean, can you even imagine Enya so much as saying anything unkind about anyone?

Personally, I prefer English swears. Wanker, tosser, bugger(er), they're quick, they're dirty, they'll usually get you in a fight... but maybe you make a friend by the end of the night.