One who explores another person's anus, with fingers, penis, or other instrument with such enthusiasm as if they were rummaging around for something in there. Also used as a playful insult of a friend, like calling them a penile perpetrator, fgt, or scrotum soldier.
"STFU you rectal rummager! I heard bout what you did to that other guy when you were drunk at the party, you fgt!"
Eric: We're headed to the pool. Be right back.
Kim: What should I do?
Eric: Diddle.
Kim: Huh?
Mark: Try the two fingered slot rumba.
Kim: Ok! (holding up two fingers.)