To beat feet means to go
somewhere quickly. It can be used as either an
explanation for having to rush some place (eg. I had to beat feet to
get there on time), or for telling someone to get away (eg. He wanted to hang out with us, but I told him to beat feet). Common term in the Army.
The
drill sergeant was yelling at me to hurry up, so I had to beat feet in order to
get there before he lost it!
This dude was
trying to hang out with me and my bros, but we told him to beat feet because he’s a nerd.