1. As an adjective, A word to describe a mean or annoying being.
2. As an insult, A word to annoy another person.
3. As an adjective, a word that describes a person who thinks he knows everything.
Meaning 1: (Man) That boy is really lumpatious (Man 2) I know right.
Meaning 2: (Boy) Ha ha Ha ha, you are so lumpatious! (Person getting insulted) Stop annoying me!
Meaning 3: (Person) I know everything, fact! (Boy) Stop being lumpatious.