I have the six issue run of Police Academy, (1989) which sticks out in my mind for its irrelevance to anything else I was collecting at the time but I went and saw most of them at the cinema as a young whipper-snapper!
I wouldn't regard titles/LS's/One-Shots such as Fallen Angels, (1987) X-Terminators, (1988) Heroes For Hope: Starring the X-Men, (1985) as being that obscure as they are linked to popular storylines/titles/ popular creators attached, at the time. Brute Force, Airwalkers etc, definitely.
I really want to locate the Marvel Fumetti Book, (1984) and The A-Team, (1984) to see what they are like.
What is the most obscure marvel comic issue/run in your collection?