There are times Heathcliff pushes Spike the wrong way or too far. and the bulldog forgets just how strong he isn't.

When Spike loses it everyone just needs to get out of his way. He never forgets who put him in that mood and he usually won't stop until he is stopped or he has destroyed the source of his aggravation.

When it's over he either forgets he did anything, or it seems like dream.

After episodes like that, Heathcliff just assumes Spike is off limits until he emerges from his yard on his own again.