A person attracted to dummasses. Dumbasses are people that are oblivious, stupid or just a dumbass in general.
(Characters are from The Owl house)
Amity, meeting a new person: Hi, I'm Dumbsexual
New Person: What?
Amity: *points at Luz who is asking what animal pink panther is*
Dumbsexual means someone is attracted to dumb people and so are they
Lilo: doi oi bahedg3rbf.
Jim: shes so pretty
Jose: Your Dumbsexual
Jim: No Im ot now stfu while i atch lilo