I have 2 DCs, including a DS who is 5 years old.
I bought some colouring hair conditioners for me and my DCs to have some fun with during lockdown, we all have blonde hair so the colours from these take really well on our hair but wash out after 3-4 washes. In case anyone is they’re a vegan product with no nasty chemicals in so no risk of damaging my DCs hair.
Today I coloured DS’s hair with an electric blue colour and he absolutely loves it. He thinks he is the coolest kid around and is convinced he looks like Sonic the Hedgehog 
He wanted to FaceTime some friends and family to show them his hair, including my DP of 4 years who has his DD11 staying with him.
DP answered and said “Oh cool, let me show DD” and passed her the phone and she immediately said “Urggghhh! You look horrible! Your hair looks so gay!”
So I hung up.
A few minutes later I get a FaceTime call back off DP’s phone and when I answered it was DP’s DD.
She was very rude and demanded to know why I hung up so I calmly said
“Because you were being unkind and rude to DS so i hung up. Also it’s horrible and homophobic to use gay as insult so please don’t use that in front of me again”.
DP then took the phone from her and tried to resume a normal conversation for a few seconds before he hurriedly said he had to go and he’d call back later. He didn’t, which is fine as he’s got his DD there and should be spending time with her anyway. I think she may have got upset after I called out her rudeness.
I sent him a text to say goodnight and I’ve been ignored.
I suspect he’s a bit annoyed that I pulled his DD up on her unkind remarks to my DS.
She has form for saying awful things, being rude and being a bully at times and I never ever say anything unless it’s aimed at me or my DCs.
She’s not a tiny child, she is going to secondary school soon and is fully aware that she what she wasn’t nice (or ok to use a homophobic slur).
WIBU to hang up and later explain why I did to his DD?
I don’t feel like I’ve done anything wrong but I suspect I’ll have to defend myself tomorrow to DP.