The inverse of a cum dumpster, a dumb cumster is a person who is down bad and willing to have sexual relations with literally anyone, regardless of an indiviual's manner, characteristics, personality or personal hygiene.
1. A pejorative to the term Cum Dumpster meaning the opposite of a female cum dumpster-hence dumb cumpster.
2. An idiotic or ignorant person.
3. A slutty girl who is dumb and takes in a lot of cum
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.