We used to dive off a boat outside Vancouver, which had a famous seal which would always come diving.
Once he got really close, and bit my mask (I got a full view of his lovely tonsils), so I gently nudged him away.
I think he got the idea I was playing, as he became exactly as was stated earlier - a frisky pup - kept bolting towards me, grabbing my arm, not biting hard, but tugging gently, biting my fins, poking his nose everywhere.
But the more I touched him, the more excited he got, until (as I was teaching at the time) he got a little too rambunctious, and I had to call the dive..
I dunno - seems like they're pretty similar in behaviour to sealions - they're cute, so its easy to forget that they can still kick the crap out of you if they wanted to..