We're here reading up to volume 2 so far meanwhile the cover for Volume 5 is posted here with Ritsu crying over someones desk or a photograph or something. Gosh I hope this doesn't get the tragedy tag.
Paraphrasing, but the cashier replied: "In that case you get a discount." when MC confirmed they're a man. This means the cashier wouldn't have given the discount if the two of them were a lesbian couple. I'd say it's fair to call it inappropriate and discriminatory at least. The rarity of same-sex couples has no bearing on that.
@Huichelaar I’m just saying that he didn’t mean any harm even though it was discriminatory. Anyone would make that mistake unless they thought about that stuff 24/7.
For example most straight couples would assume others are also straight. They mean no harm by this though.
Also keep in mind these aren't our humans and we don't know how that changes things. Like posters for previous chapters commented "they forgot intersex?" well that might not actually exist in this setting.
Everyone knows that straight couple is the most general. The cashier's not at fault for assuming, and same-sex couple shouldn't feel discriminated for that. Things would be different if the cashier denied them AFTER knowing that they're a same-sex couple.
@NenjyN well the guy being forceful since he overheard his big bro saying no genderless person live pass twenty.
@Zeesnowflower2002 that gonna be hard. i don't think there is that 'accept them regardless their gender' concept in that universe. or maybe the author hasn't show em yet