I (24F) went to my boyfriend's (30M) family's place for Christmas and I think I ruined Christmas by "pouting"?

I need help trying to understand if I need to lighten up or if my boyfriend?s family took it a step too far during Christmas dinner.
My boyfriend?s family has a very close-knit family who loves to play games together, drink and have a good time. They also like to rag on each other from time to time, which generally is all in good spirit. However, I felt like this year his family took it way too far, but my boyfriend thinks I need to ?lighten up because it was unacceptable I spent the entirety of Christmas pouting.?
So for Christmas we all gathered at my boyfriend?s parents, and everyone was having a good time. I was mock singing to Christmas music with my SIL?s (34F) (just easier to call her that even though my bf and I aren?t married) pre-teen/teenage kids, and generally being big and loud and silly, which everyone was getting in on.
About an hour later, we all gathered around the table to play a board game, where my SIL commented about how she was feeling pretty drunk already. We all laughed and started to play the game.
I?m not sure what changed, but suddenly my SIL started commenting on my horrible Christmas singing and mocking some of the higher notes I was making, which of course because it was all in good fun, I decided to hit one again (I know this is stupid).
My SIL winced and began mocking my singing again, which was still all in good fun and everyone else was joining in too. My SIL then started mocking my accent and how silly it sounded, and her teenage kids started to mock it too. I found this mildly offensive, but I played it off because sometimes I do say things a little funny and it was clear my SIL was very drunk.
The game continued, but for some reason my SIL wouldn?t let up. She began asking me personal questions about me going to university. I told her that I was relieved for the break because I just finished a major presentation for one of my classes, which I was stressed about.
My SIL then asked me ?Oh, did your classmates ask for subtitles while you were presenting?? And everyone in my boyfriend?s family started howling with laughter, but I became really really offended by this and needed to clear my head.
I excused myself and got up to smoke, but from the other room I could hear my SIL still berating me, and she turned to someone at the table and said ?my GOD her voice is annoying! I wish she would just stop talking sometimes?
When I got outside, I called a friend to wish them a Merry Christmas and to loosen up a little and to calm down. I was out in the family?s garage for about 20 minutes until I felt better enough to go back in, but by that time I didn?t really feel like partying anymore.
I was mostly silent the rest of Christmas and through dinner, and my boyfriend?s family was starting to notice and comment on. They were jokingly saying ?lighten up? and ?are you a sore loser?? because I had lost the board game. The kids still hadn?t let go of my accent, and kept asking me to say certain words, until my SIL hushed them sternly.
By the end of Christmas dinner, you could hear a pin drop in the room, and I sort of spiraled from there because I realized that I was actually pretty hurt, and the silence met with more teasing was becoming more and more awkward and embarrassing for me.
After dinner wrapped up, I helped my MIL in the kitchen with the dishes where her and I had a normal conversation, just chatting lightly. Afterwards, I went to my boyfriend and asked if we could go, which he accepted because he felt something was off.
After the goodbyes, my boyfriend and I were talking in the car. He was asking me what was wrong, and if someone had called me with bad news (because he saw me talking on the phone in the garage). I told him no, but that I felt his sister had taken it way too far.
Suddenly my boyfriend was annoyed with me. He told me he didn?t understand why I couldn?t just roll with the punches, and told me to ?lighten up because it was unacceptable I spent the entirety of Christmas pouting? and that ?his family had gotten really concerned that something had happened to me.?
I exploded on my boyfriend then and told him to take me to my parents? instead of back to our apartment, which he did. He tried to apologize and walk me to the door, but I told him that I didn?t feel like being in a relationship with a racist and his racist family, which I didn?t really mean. I was just really really mad at the moment.
I woke up this morning and had breakfast with my family. I started feeling a little better, and checked my phone to see that my boyfriend and his family had texted me a bunch of times. His sister has texted me a big long apology.
I haven?t responded to any of them yet. I?m hurt, embarrassed and I feel like I ruined Christmas for them.
Any insight is very much appreciated.
TL;DR During Christmas, my SIL started to tease me, but she took it too far when she started mocking my accent and the rest of the family joined in. I shut down, Christmas became awkward and my boyfriend told me I really needed to ?lighten up?. I?m not sure how to handle the situation.


Source.