I think that '莲' literally means "lotus" but I heard some people saying that it also has a bad meaning, if somebody calls you like that you should be offended. Can someone explain me why? Thank you so much.
i'm afraid there's no such bad meaning with 莲 in chinese,actually it's not a common word in daily life as it is not commonly seen.
however i'd say there's indeed a bad meaning if you insisted,莲 as a component of 白莲花 has two completely different senses of bitch and pure girl.the former implies someone pretending and trying to make others believe her a pure one.
in other way you can also take it as homonym in 不要逼脸 which transform to 不要碧莲 that actually means 不要脸 or merely a joking phrase。