I learned the elbow flick the same, but the folks who pat their hip are always doing it as a preface to sweeping their hand across their backside to indicate a pedestrian or a car ahead on the shoulder or in the lane being ridden in and that they will be pulling out to avoid it. Often accompanied by calling out "runner up" or "car up" as well. I kinda see how it means "follow me," just never seen it used for general purposes or in any other circumstance.

When I rode motorcycles, a buddy and I used the signal of slapping the thigh to mean "I'm about to accelerate" (i.e., giddy-up! ) Along those lines, the most misunderstood signal I've seen was when a ride leader raised his hand above his head and waved it in a circle. We were on a usual and familiar course, so it definitely didn't mean "we're turning around," for which I'd seen a similar gesture. It looked rather like he was cracking a whip, which I took to mean that we should (get ready to) sprint for the town line which happened to be ahead. What he intended, however, was to indicate something like rounding up, or for everyone to close their gaps (we'd gotten sort of stretched out back at an intersection). Of course the exact opposite happened as some of us just started hammering.

One signal/flourish that nobody taught me and I don't think I've seen anyone else use, but which I like to use is an upward swooping movement of the arm when indicating a turn to highlight the fact that we're turning directly onto a significant incline. Similarly, a hand reaching forward and up to indicate "climb ahead," undulating to indicate "rollers ahead," or up then sharply down to indicate "crest and steep descent ahead." Pretty obvious, I think. People might wonder why or what it means at first, but I doubt they mistake it for something unintended. Would you?