What does Heathcliff say he will do to Edgar if he threatens him?

Catherine and Heathcliff have a meeting in the kitchen of Thrushcross Grange. Edgar Linton comes storming in, leaving two male employees he has brought with him in the passage. He arrives as Catherine is scolding Heathcliff. In a state of annoyance, Edgar tells Catherine that he will no longer have a low ruffian and "moral poison" like Heathcliff in his house. Edgar threatens that if Heathcliff does not leave within three minutes, he will have his men forcibly throw him out.
Heathcliff is not in the least intimidated by Edgar's threats. Nelly Dean records Heathcliff as doing and saying the following:

Heathcliff measured the height and breadth of the speaker with an eye full of derision.
"Cathy, this lamb of yours threatens like a bull!" he said. "It is in danger of splitting its skull against my knuckles. By God!  Mr. Linton, I’m mortally sorry that you are not worth knocking down!"

Heathcliff has responded to Edgar by saying that Edgar is beneath his contempt, not even worth striking. He goes on to say, however, that he would be willing to kick Edgar like a dog:

I would not strike him with my fist, but I’d kick him with my foot, and experience considerable satisfaction. Is he weeping, or is he going to faint for fear?

Heathcliff shows that Edgar's threats mean nothing to him. He reveals that he considers Edgar a worthless coward.