1) One who engages in the practice of exploring the anus and rectal passage of another, just as a spelunker enjoys exploring dark, dank, underground passages.
2) A person who acts as though he might enjoy the practice of ass spelunking.
1) Man that guy is an ass spelunker. I think I saw him in the Gay Pride Parade last week.
2) Goddamnit Jimmy, stop prancing around like a fucking ass spelunker.