This 6 episode OVA from 1991, Inferious Wakusei Senshi Gaiden Condition Green, might be the worst anime made in 1991. Its one of those anime that somehow gets objectively worse the further in it you get, and the moment you finish it, you realize just how bad it is.

Objectively terrible, some of the voice acting sounded amateurish, animation gets worse each episode, story is completely forgettable, I barely remember anything about it other then some green alien bad guy thing, but there is one thing I couldn't forget.

Its WTF ending. Not only is it all a ridiculously rushed conclusion, but from what I remember, one of the major characters gets on the alien ship, and I think he is trying to hack it or something, so then he actives some bombs, he makes a stupid face doing it, then suddenly it explodes and the explosion reaches the main alien bad guy and kills him. Then it just ends. Like WTF happened.