There's another thread going at the moment with similar sentiments being expressed. I'm not sure of the etiquette about duplicating examples of a concept relevant to both threads but the following seems relevant to this discussion.

Some years ago I was at an instrumental session in the main bar of the pub in Kapunda, South Australia. There were lots of instrumentalists there, from all over southeastern Australia and the place was rockin' along when an Adelaide local (who'd recently acquired a 6-row Continental system button accordion) started playing the Athol Highlanders. For some reason, the tradition in Adelaide has this tune played in G, whereas most of the rest of Australia plays it in A.

To make sense of the rest of this story you'd have to understand the layout of the Continental system keyboard, where, if you learn a tune on just three rows, you can transfer the same fingering up, down and across all the rows and play that tune in every key known. It would also be helpful to know that the Athol Highlanders is played in Australia at a rather cracking pace.

Your man played in G and we all joined in. Some of us already knew the SA tradition and were prepared but most others could cope. After a couple of times through, most of the rest of us launched into a repeat with the tune in A; everybody joined in. After the regular 'twice through' someone started it in D and again most of us kept up. Your man then decided he was going to take the tune through every major key. It was easy for him as all he had to do was transfer the same fingering to slightly different parts of the keyboard. All the rest of us, except one, dropped out.

Bronnie Evans was new to the folk scene at that time but, even though she'd been playing whistle for only a month or two, she was a red hot whistle player. This was probably because she'd had ten years' classical training as a flautist, although I suspect I was one of only three people in the bar who knew this. Bronnie had been playing her flute when this session started and, even though the Athol Highlanders was new to her, she joined in with a will and played quite competently when the rest of us were playing as well.

When your man started 'playing the smart-arse', so to speak she would cock her ear to pick what key it was he's got into, for the first bar or so, and then rip into playing along with him at the same cracking pace. She kept up with him for every key change. At the end of it there was wild applause, all of it for Bronnie.

In that example I'd probably agree your man was showing off but he's normally a really good and considerate session player and I think he was just rather excited about having got on top of the Continental-system keyboard.

Cheers, Rowan