Noun: An undesirable person or object that is unwanted and rejected.
Adjective: Used to describe someone's repulsiveness. (For lack of better words)
Example 1: "Hey Jim! How was your date?"
Jim: "Dude... She was a straight up trashboat. I couldn't even eat."
Example 2: "Don't bring that trashboat to my party bro, or I'll fuck your sister."