If his fins are clean imo its likely dominance related.. the term "Tank banger" didn't result from fish that like to head bang.. some particularly aggressive fish will litteraly bang into the tank walls due to aggression. cichlids are notoriouse for this. i would try moving your deco around or changeing it up abit to give him something to do other that smash his face against the glass... which btw can do some damage, sometimes fatally. particularly if an open sore from rubbing gets infected. I had an Oscar that did this until I gave him some caves to explore and lord over.
