Dave Stallard wrote:

I'd recommend a stationary bike in a gym.

At 500 lbs, riding a regular bike is not safe for him or for others
sharing the road with him.

Don't be a prick. He's far less of a hazard to other road users than
anyone in a car.

Bikes can be made to serve people of different sizes, fortunately.

Be thankful that this is an electronic forum; any 500-pound person who
is strong enough to pretzel his cranks could also wrench your puny
limbs until you squealed like a little piggy.

Chalo Colina