They certainly can be. If you ask 100 people if behaviour x is harassment at the minor end you will get a lot of variation. As I mentioned before I was technically sexually harassed many times when I was younger, but I would not consider myself to have been sexually harassed purely because it was so minor in my mind. A lot of it was just playful banter that went too far, but some of it was more than this and not pleasant. In the greater scheme of bad things that have happened to me in life it was not important.

What is much more of a problem in academia is abuse of power. Academics have huge power and unfortunately far to many abuse this power at the expense of their students and postdocs.