It's hard to call them good manners when he went ahead and stole the cake anyway. Add continues to frown, but if he can still have his twice-stolen cake slice, he'll remain content for now. He'll let it slide this time.

He doesn't actually have any space left on his plate to put down this cake slice, though... He nudges the mochi pile into a taller stack with his fork, still holding the cake-bearing knife awkwardly. This is too much work for one slice of cake.

"I wasn't aware that was something thieves cared about, but no matter. Does the god of thieves have a name?"