Sussy is derived from an abbreviation commonly found in the popular Murder Mystery RPG "Among Us". There, the usage of the term "sus", an abbreviation of "suspicious", is used to indicate to other players that a certain player has taken the role of the "Impostor", a role that gives the player or players who have it the ability to kill Crewmates in order to win. The crewmates can vote the impostors out, but need to be careful since the Impostors are trying to stay hidden and frame other players as the Impostor. Therefore, the first part of the phrase "Sussy Baka" is indicating suspicious behaviour on the Subject's side.
The term "baka" is a Japanese word, written in Romaji. The direct translation goes along the lines of "idiot". It is often used in modern media to insult or play with one's feelings, though it is more regularly used in a more relaxed manner. One such example of this would be the phrase "Sussy Baka". In the case of that phrase, it is often used to suggest that the Subject is acting strange, often with slight sexual connotation.
