A portmantaeu of "gangster" and "monstrosity", the word gangstrosity refers to something that is unbelievably cool, badass, and unique. Something that is a gangstrosity often inspires excitement and high-grade creative output. One usually gets "hyped" on something that is a gangstrosity. One does not simply obverse the awesomeness of a gangstrosity, but is compelled to act on the resulting inspiration.
Those lyrics are such a gangstrosity! I think I'll have to make a song out of them!