Do you think its rude to eat with your elbow(s) on the table? Why?

My mom keeps telling me not to eat with my elbow(s) on the table because apparently it’s “rude.” I don’t really understand why since sometimes the sharp edge of the table hurts my forearms and sometimes I just like to rest my arm on the table so I don’t feel uncomfortable. But apparently it’s “okay” when i’m finished eating… When I ask why she keeps telling me it’s rude she just says she doesn’t know and does it because she was raised that way but I just keep thinking it’s really silly. I tell her it’s just as silly as saying it’s rude to drink your glass with your left hand or wipe your mouth with a napkin with your right hand but she refuses to change her opinion.

Am I missing something? Do you tell the same to your kids? Why?