I think its more the fact that he gives that "scheming evil brother vibe" you know the one.
The one where in almost every show the little bro acts all nice
And gentle but in reality he is a smug/douchy lil shit.
He hasnt show us anything , but past shows and the fact that weiss acted like a complete bitch at the start of vol 1 gives us this "hes gunna be a cunt" vibe.

>-fuck Weiss and take her place as heir of the company
Isn't he her brother or something?

…Well Monty did say he was a Game of Thrones fan.