what was with the line "I always wanted to do that" at the beginning?

Coach Willis and Mrs Olson both say that after they attack Miss Drake, as if its a line the aliens are always gonna say after they kill someone, like their catch phrase or something. But the line is never uttered again after the opening by any of the aliens. And that line is never really explained, why did the aliens always want to do that? Was they expressing the inner feelings of the hosts they was in like they always hated Drake and thought about killing her?

I just always thought that was odd both of them say that in the opening but none of the other aliens ever say it again.