Not By Lies
they pollute the information environment
A friend once told me about a quirk of girl-code in her friendgroup: whenever one of the girls got a new boyfriend, it was obligatory for all the other girls to say 1) how great and attractive he was, plus 2) an inoffensive reason why she would never be able to date him. E.g. "oh wow, Alfred is so great – funny and kind! But I could never date him, I can't do men who have dogs." The concept was (approximately) to assure everyone that you weren't a threat towards their partners.
But my instinct on hearing this was: come on guys, you're polluting the information environment! What if your friend runs into someone who seems perfect for you, and she's about to introduce you, but then it turns out he has a dog, and you've made up this nonsense about not-liking dog-guys, so she doesn't? Wouldn't it be better for everyone if you just said "hey your boyfriend is great in every way, but also I'm a loyal friend and OF COURSE I will not hit on your boyfriend, regardless of whether I might abstractly have gone for him otherwise?"
In a sense this is a mirror of the carrot problem: every lie you tell in life has an additional consequence of polluting the information environment, which is independently bad.
If you must tell lies, I think it's important to design them to be minimally information-polluting. Which I think in this case means they have to be 1) only applicable to you, 2) judgeable only by you. E.g. "oh Alfred is so wonderful, but I could never date him myself because his aura is too purple. I am not answering questions at this time about how to evaluate the colors of people's auras; if you meet someone seemingly-similar to him please send them my way."