[He says this to Tanjiro after hearing him complain about slicing a boulder. He is angry that a student of his former teacher would give up so easily.]

Impossible? I thought the same thing when I had to do it. But I still sliced through that boulder!

[Angered in the middle of his fight with Tanjiro. He is almost appalled at the lack of proper swordsmanship from Tanjiro.] 

What the hell is that form?! What has Urokodaki taught you?!

[Almost excited at the thought of the challenge he has ahead in training Tanjiro.]

You’re even worse off than we thought.