Why is that weird?

In class, we have been talking about social deviance. Deviance is the act of doing something "weird" or different. In sociology, it is okay to do something unnormal, but in the world, people look at you differently. Not all acts of deviance are bad though. We read a story about a man who did an act of deviance and ended up helping a man out of a slump in his life.
We were then encouraged to do an act of deviance in our life, so I thought I would do something to help my friends. I don't normally go out of my way to help my friends, because I have a casual relationship with all of my friends. So, when we were at lunch last week, I decided to do my act of deviance. I did something simple, because I didn't want my friends to be too weirded out. So after we finished eating, I stood up and threw away everyone's trash and put the trays where they are supposed to go. My friends all told me that I didn't have to do that, and they seemed kind of uncomfortable to have me do something so simple for them. One of them even told me to stop because she could do it! I just continued on, and told her not to worry about it. After I threw everyone's stuff away, life went on like nothing had happened. They were all thrown off for a second, but after it was over, life went back to normal.
Why do things that are done just to help people have to be weird? Why can't it be okay to help your friends out once in a while? I don't want it to be weird! I just want to help my friends out, and not have them think that it is weird, especially in a bad way.