Learn Japanese with Anime - You F**kin' Traitor!

Analysis

この is a pronoun meaning “this” always followed by a noun so as an example, このいぬ means “this dog”. But when the following noun has a negative meaning, and when it’s said to the second person it just means “You” showing expression of frustration or anger.

うらぎりもん actually comes from うらぎりもの which means “traitor”. The verb うらぎる is “to betray” and もの is “a person”, which makes うらぎりもの “a person who betrays”, hence “a traitor”. But Eren shortened もの and turned it into もん which sounds more aggressive.

が: I think a lot of people learned this particle as a subject particle, for example, 天気がいい meaning “the weather is good”. But this が after a noun with a negative meaning implies swearing or expression of anger. It is also important to note that in this usage, you do not continue the sentence after が.