Great thread, and some fascinating interactions you've had! We've certainly seen a lot of "play" behavior in local harbor seals, who I'm sure see no shortage of divers. Generally, I never go as far as to extend a hand or actively reach for them, I just allow them to do whatever they want (usually, nip on fins, tug on hoods, dart all around) and put my hand up as a shield if needed. We've been buzzed and head-faked by big sea lions before, but have never seen any aggressive behavior towards us by the seals. I have seen an underwater "disagreement" between seals that had us running for cover (how much protection would a kelp holdfast really be?), but it's enough to make me happy to appreciate them from a distance when they choose to stay away.