The worst kind are those who attack you with an inferior stack (2 Klerouchon Agema plus some crap unit vs your own, well-balanced full stack ), then withdraw through their own infantry unit, thereby escaping you (thanks to the engine's most retarded feature - auto-engage, which makes your pursuing cavalry fight the infantry unit instead). Then they come back, with a full stack of mercenaries they've conjured out of thin air.
I've even used assassins once or twice on these cretins, although I generally never use them on generals. But it's just so bloody annoying.