And you also never met me (I am a guy too).
My response to unexpected fist bumps, high fives and handshakes is basically a silent "Huh?" before I figure out how to respond. Awkward 4 seconds. Oh, and I also likely forgot what I was thinking of and won't have a peace of mind until I remember it to finish the thought, but that has nothing to do with actually doing a high-five or not.