Never feed them after midnight. Meaning she doesn't sleep over ...
Barney: How do you keep a girl from becoming your girlfriend? Simple, the rules for girls are the same as gremlins. Rule number one: never get them wet. In otherwards, don't let her take a shower in your place. Rule number two: keep them away from sunlight. i.e don't ever see them during the day. And rule number three: never feed them after midnight. Meaning she doesn't sleep over and you don't have breakfast with her, ever
Ted: What about brunch? Is brunch cool?
Barney: No Ted, brunch is not cool