It's just me and my teenager here, so we pick the holidays we go on together, so they are always places she approves of.
And basically I don't ask a lot of her, she can be on her phone pretty much whenever, she can sleep late, I probably spoil her a bit with food/money etc. She's a really good girl who works hard all year, and it's her holiday too! Because of this, we tend to get on really well. She does need some emotional space tho, we both do. Currently we are sitting in a pub, both on our phones, happily chilling..... Haven't spoken much to each other in the last half hour.....
I appreciate it's much easier as it's just me and her - much harder if you have more adults and kids to consider. My generally sweet natured girl bitches a lot to me about the holidays she is taken on by her dad, his partner, her kids and sometimes other extended family members!
(At the risk of sounding judgemental, I do think it sounds like exh's gf makes it harder on herself by doing lots of "organised fun", banning all the teens present from their phones for big chunks of time etc. I mean, it's her choice ultimately, and i know many on here would see that as good parenting and think I am way too lax, but i just think, is it really a hill worth dying on....)
However OP, despite my general laissez faire attitude I do think it sounds like your teen is taking it too far by being actively rude to you. I have no doubt DD makes her dislike for her blended family holidays clear via her resting bitch face, but she wouldn't be actively verbally rude to XH and partber when they are paying to take her away.
Your teen doesn't have to pretend to enjoy it, but he shouldn't actively ruin it for everyone else - that's just unnecessary in my opinion .