A statement that something doesn't make much sense. It's a shortened form of the concept "try to figure that one out."
Mr. Wong: Yes, Wong very racist. Don't like black. Don't like Jew either. But black and Jew love Chinese food. Go figure.
A complex manouevre that involves closing one eye whilst keeping the other one open.
The Doctor: Since encountering the Weeping Angels, I've been trying to come up with a counter-measure, and I've finally figured one out.
The Doctor: I call it 'blonking'.
The Doctor: Of course, it's probably only Time Lords who can do it.