One weekend a few years ago, when my siblings were hanging out, we rented a movie as we are apt to do. Some families talk or play games or do sport activities. We see that as a waste when we could be watching Star Wars for the 957th time.
Being that Lyn and I were really into CSI at the time, our brother brought home To Live and Die in L.A. with William Pederson. It was a strange movie that wasn't very good. We watched anyway and then were confronted with a bizarrely frightening sex scene where you actually see William's more intimate bits. The movie did not get better from there.
We were all talking about the evening a day or so later, when one of the group said "I think the trump card of the evening was having to see Grissom's wang." From then on, we called it "his trump card". It's been a running joke since then.
Apparently, it's started to catch on across the globe. I just received a spam email encouraging people to "Whip out your trump card".