nunbeater's post was good, as well.
You don't need to specifically point out the fat guy, as he is literally the elephant in the room.
You just need to go to the tournament director and tell him/her that, given the circumstances at the table, you cannot play properly, as there is simply not enough room for 10 people.
Consider this: What if, by coincidence, 10 obese people were seated at the same table? They literally could not fit. This is a less extreme version of that circumstance.