Quick Definition: A semi-conscious reaction to a surprising or less than normal sight, in which someone casually sees something, briefly stops looking at it, realizes what it is, and snaps attention back to it with an expression of surprise or disbelief.
Many AFCs, and even some PUAs, will do double-takes when a really hot girl walks by. This usually signifies low status behavior, whereby the beauty of the HB walking is conveyed to be interesting to the PUA. Paradoxically, if an AFC pretends to not see the girl, or if the situation is so weird (i.e. obvious hooker in Vegas) and it is obvious the AFC is uncomfortable in looking directly at the phenomenon, it also conveys low value.
Interestingly, most of the time, the person with the highest value at an event will turn to face a new action/event with the slowest and most subtle gaze. Little catches the surprise of James Bond or Donald Trump, as they are always in the know. Double-takes are thus good to use when the PUA conveys high value by using it with a slow eye gaze and a sense of ease, and bad when they are used as a strong surprised reaction to another person or event of higher value.
I like it when a girl does a double-take on me when I walk through the club.