Actually, the question, "should someone be able to sue over ???" isn't really applicable in our society. I'm not a lawyer but having been involved in litigation numerous times I've listened to a lot of lawyers and worked with lots of them, in addition my baccalaureate required I listen to lawyer professors, however, I've forgotten most of that.
What I do recall though is the advice that in the US "anybody can sue anybody for anything anytime". The germane question though is, if someone sues, "what are the odds of them prevailing?" If someone sues willy nilly because they simply have a litigious personality, it is possible that they lose a lot of money in the process of losing. They have to pay their own court costs and legal representatives and in most cases pick up a sizable share of the prevailing parties expenses; for the most part, frivolous lawsuits are rare due to that eventuality.
Truth is the plaintiff could and does often lose everything they have if they undertake a stupid lawsuit. Unfortunately, in our society we have some who possess obscene levels of wealth, losing doesn't mean much to them, they simply write it off. So there exists the rare chance that one can get legally hammered by one of those dudes simply because they don't like the way someone parts their hair.