To do something for one quick second but you sayin one time, that doesn't really mean one time. A Lowkey activity or scheme should be mentioned to all involved parties as doing it for the "one time". But it's just something either Lowkey as hell or an activity you do once a week. A daily activity is NOT for the one time.

Doing something just to try it, even if you only do it once and never again; for the sake of adventure.

...you know, when you did that that one thing.

The police. So called because you look one time at them, as doing a double-take might attract attention.

The cops. It's correct that it means looking more than once can draw attention. But the actual phrase comes from someone saying "one time" to let the other passengers or friends know that they have now seen the cops and are claiming the first look, and no one else should now turn around because two or more people looking increase your odds of being stopped by more than 50%.

When you yeet on somebody too hard, and they get upset, to let them know it was a one time thing and you won't ever nae nae on them or hit that soulja boy in their face ever again, you tell them it was jus one time for the one time