'Being ugly' is, in some places (like Texas), a term used to describe the actions of someone who is acting rudely/unpleasantly to others.
While 'being ugly' is a common phrasing, there are other variants, like 'acting ugly', 'are/were ugly', and so on.
"Grant, stop being ugly to your little sister and behave!"
"I can be a really ugly guy when I go without smoke break, man."
"Sorry about my mom acting so ugly to you during dad's funeral."
"S'alright. I acted pretty ugly to him while he was alive, so I understand why she'd do the same to me while she was grieving."