AITA for not wanting people to pee in my shower?

I (21F) hosted a house party to celebrate the end of semester for a bunch of people I go to college with. The turnout was actually a lot higher than I expected, there were probably over 100+ people there, and only a handful (maybe 30-40) were my friends, others were strangers or mutual friends from my college. I didn’t really mind too much since my house and backyard are pretty big, it’s just that we only have two bathrooms.

At some point in time I went inside because I needed to go to the toilet. The first bathroom was locked with a pretty long line up outside, so I went to the second one. I was surprised that the door was open and peeked my head inside to find that there were a bunch of people in there. I at first thought they may have been doing some drugs or something so went in to see what was happening.

There was one guy sitting on the toilet pooping, and then probably 3-4 guys standing around the shower. My shower is a combined bathtub/shower, and they were essentially using it as a urinal, all peeing into it at once. One of them finished up, and another guy took his place peeing into the tub.

I was quite peeved, and asked the guy that had finished up why he thought that was an okay thing to do. He said it’s pretty common and he’s done it heaps of times before to save time. He also said it’s pretty easy to clean and makes things easier. He said some of the other guys had been pissing outside but that, since my yard didn’t have any "natural" spaces (i.e., grass, bushes) that were out of view, the only option was to pee on the pavement around the side of the house or the wall of the house.

I think that it’s just gross and disrespectful to me? I feel like they’re just treating me with no respect by doing this. Is this normal? AITA for not wanting them to pee in my shower and are they TA for doing so without asking permission?