Argument with parents about dinner

This is such a dumb situation but I need to vent about this nonsense. I started dating a girl a couple months ago. My parents are yet to have met her mainly because I've been trying my best to shield her from them.

I'm going to graduate uni this weekend, so they've decided to come into town and make the whole event about them. I don't want to go to graduation, but they insist because it would make them look bad if I don't go. Ok. Whatever. They're insisting they have dinner with me and the girlfriend. She's a vegetarian.

At first, they suggested we go to a steakhouse. I love steak, but I also want my girlfriend to be able to eat. I asked what is she supposed to eat. My mother told me that she can piece together a meal of fries and broccoli. Wow. What a nice night out!

After protesting, she keeps changing the plans to other steakhouses. I don't know if she realizes what vegetarian means, so I keep pointing out that there needs to be at least one entree that doesn't contain meat. They're irritated by that. I was told that "she chose to be vegetarian so she's going to have to suck it up occasionally" and "Your girl needs to fit into our world. I'm sorry, but your family always comes before some girl" (not exact words but I'm translating old person leetspeak to English here).

That's all irritating on it's own. She's the guest at our family events, which means she should get some priority. But the thing that killed me was when I was told that my girlfriend is changing me. Either that means that I've always been a shithead who never gave a damn about anyone else or they're just throwing mean words to try to get me to back down. I'm just so irritated by all this.

But to end the story, we agreed on a restaurant that my parents love, I hate and has vegetarian meals. But I love how I'm the bad guy for wanting my graduation to fall into line with what I want. My graduation is a day for them to show off what they (really, I) did. They told me when I first started in college that I was too dumb for my degree.

tl;dr Fought about dinner and told I'm a bad person because I respect my girlfriend.