When you put yourself down. “I’m not that pretty.” “My hair looks like crap.” Or whatever, particularly after you received a compliment, you are insulting that person or the people who love, care, and/or admire you. You are saying that they are lying sacks of shit.
People take the time to give you nice feedback, take it to heart. Don’t challenge their honesty. You’re insulting them. They love you more than you love yourself. There’s an issue there.