Being called nice

Throughout my life, I've been called a gentle giant or just a nice person. Certainly those are nice compliments, but for me, it's one of my only ways to express myself. I'm also a docile person, but when I tried being an aggressive person, the results are never pretty. Sometimes, I don't know how to act around people besides just being nice to them. I can be sassy at times, but I have to be in the mood to act that way.