Someone **YOU** who looks up the definition for "dumbass" on a dictionary.
You're the dumbass, YOU.
A person who looks up the definition of Dumbass
Josh is such a dumbass, he left his tailgate down while on the highway!
Someone who has to look up the word dumbass
Person: What’s a dumbass
Other person: You’re a great example of one
A dumbass is the person taking time and effort to go onto urban dictionary to search dumbass, in other words you are a dumbass