Trip is usually tolerant, as minor insults like telling him to shut up, or saying obscenities cause him to attempt to laugh it off saying "Ha, never afraid to push our buttons, ha ha ha, heh...", or may cause Grace to intervene by saying "that was just a little poke in the ribs between friends".
if the player says "melon" during the early stage of the game before trip and grace start fighting, it will fall into the "strike system" where the player can say it up to 3 times before getting kicked out. if the player says it after trip and grace have started fighting, it will result in an immediate ejection from the house, regardless of if they have said it before. during the end game stage after either trip or grace reveals their secret, nothing the player says will result in them getting kicked out.
The word melon is a slang term to refer to the female breasts, and could be interpreted as an obscenity, as mentioning other slang terms causes a similar reaction from Trip. Although the game never explains why trip has such a deep hatred for melons, so the definitive reason is unknown.