don't look now

A warning used when the speaker wants the listener to be aware of someone out of their field of vision, without having them turn around and conspicuously look at the person. Don't look now, but your ex just walked in. A: "Don't look now, but—hey, why did you turn around? I said not to look!" B: "I can't not look when you say something like that!" Don't look now, but there's a cute guy making his way over to us!