He doesn't actually consider Adric a threat. He's just spouting bullshit to provoke the man under his foot. But the words that come out....

He laughs. Long and hard, and maybe a touch insane if you listen closely. The grin on his face is bright and razor sharp, full of amusement but not at all kind.

"Oh, really? I killed the Doctor? Tell me, are you some traveler from the future? A loyal lapdog of that man aiming to kill me?" He presses his foot down a little harder, enough to push the breath out of Adric's lungs. "You should have at least sent a fighter if that's what you wanted."