People get too hung up on what bike is suitable for bigger chaps. I'm 19 1/2 stone and ride all sorts of bikes – a light Ti 29er hardtail, a cross bike, a 7" full susser and a steel singlespeed without any problems. I always ride air forks and shocks as springs don't really go up to suitable weights and I don't spec my bikes with anything silly light, just good reliable kit from manufacturers I trust. They're all in the sensibly light range for the type of bike though.
As with all bikes/components, sometimes things fail but riders **** them up themselves is far more common regardless of how much the rider weighs.
All the above is useless though if your chubster mate can't handle a bike and will go crashing into every obstacle on the trail with the finesse of a pi55ed hippo on rollerskates.