Tev only responds to that sort of thing during and immediately after violence, so:

Take him out to kill dudes, kill a bunch of dudes, and then start putting the moves on him. (You can start putting the moves on him while you’re killing dudes, if that is not too distracting for you.)

(Logistically) Eaiser method: Assuming you can actually fight a death knight and not die: Challenge him to a fight and then start seducing him.