Is it normal to be called a slut by people you don't know?

Most likely because you're dressing in a way that seems trashy or slutty to them.

You can't expect to dress a certain way and think nobody will make comments if you look a certain way.

You wouldn't expect nobody to say anything if you seen a transvestite walking down the street in women's clothing and make up.

I myself when in England got shouted "Hiya, Queen" because of the long hair I had. The majority of men had skin heads, and anything different wasn't considered normal. I knew that when I was in the enviroment even before they shouted that. They had a reason, the majority of people didn't dress or have the same style as me, so obviously I was going to be seen different in positive and negative ways.

You obviously must of been wearing something to make them think such things. Does that make it right? No, it is understandable, though.

My advice, don't dress the way you were when they said it to you if you get upset about it.