Let me just describe my behaviour. I have a military haircut and a somewhat aggressive demeanor, and I wear weightlifting gloves.Goodness.
I bring a duffel bag to the playing hall with me, containing my chess gear and two dumbells, one 40-pounder and one 50-pounder.
Once our game is underway I take out the 50-pounder on my opponent's time and begin to do bicep curls under the table. It's all out of sight, but from the strain on my face and the motion my opponent knows what I'm doing. Still, it's fairly discrete, so nobody complains.
After a few sets on each side (one set per move, always on my opponent's move) my opponent has obviously passed the point of objection and has resigned himself to my behaviour.
That's when I switch from the 50-pounder and curls to the 40-pounder and tricep extensions, which are obviously above my head and therefore much more distracting. But what is the poor guy to do, since he has already accepted his opponent's working out during a game?
For me, it actually helps my concentration, as I have nervous disorders which are alleviated by the exertion and adrenaline. For my opponents it may be another matter, though none have dared complain.
Now, normally with a post heavy on the quoting like this one, I'd just provide the relevant link for readers to explore further from, and that'd be it. But here, a bit more explanation is required. Bear with me, if you please...
The above quotation was originally published on PawnPusher, a website dedicated to "chess humour, sarcasm and theory". The site was written by Darren Jones and included sections such as "Amazing & Untrue Chess Facts", "Chess Metaphor Liberation Organization", and "Scumbag Tricks" - from which the above was naturally taken. However, by 2004 Darren was no longer updating PawnPusher. The url lapsed and a domain squatter moved in.
But all is not lost. The Internet Archive is a website that has recorded "85 billion web pages ... from 1996 to a few months ago". They provide a "Wayback Machine" which allows anyone to browse internet pages from years ago. Meaning, the Wayback Machine can be used to access PawnPusher from before the domain squatter moved in. And so, to cut a long story short, the rather strange-looking url for the above quote is this one. All archived PawnPusher pages can be reached from here. The first archived edition is here, the final one before the domain squatter moved in, here.
Have fun exploring...
Thanks to Kingscrusher of Chess World for the tip.