Couple factors come to mind....
Filling the tank - I fill mine until the fuel is at the bottom of the filler neck. Then I'll add more. Then add more after the gas "settles" and fills air pockets in the tank. Do this a few times and it makes a difference how much gas you can get in the tank. Possible you and your friend don't put gas in the same way.
Besides possibly one plug not firing (coil, fouled plug)....when was the last time you serviced your bike? Could require carb sync, air filter.... This would impact mileage, as would when you shift gears. Lugging the motor or going to 5th too soon would lower your mileage too.