Charge them for everything:

The single most important element in the success of a business is the relationship with its customer. Perhaps no business has a worse customer relationship reputation than the airline industry. Today there is a story in the Chicago Tribune which further expands the guest service mantra so prevalent in the industry.

One thing we have looked at in the past, and are looking at again, is the possibility of maybe putting a coin slot on the toilet door, so that people might have to actually spend a pound to 'spend a penny' in future," O'Leary said, using a British euphemism for going to the bathroom.

First the extra bag charge, then the first bag charge, then the overweight charge, then the beverage charge, then the pillow charge, now the potty charge, and I am quite certain that there will be a charge for pressurized oxygen (O2) in the very near future. If you can delineate the charges certainly that will lead to lower fares for everyone. From personal experience I know that I rarely use anywhere near the amount of O2 that other passengers use. Why should I pay for their extra O2. The concept is very similar to separate checks, why split the check if we can have separate checks. Actually, why not charge people based on whether their sleeping, talking to other passengers or better yet talking to an airline rep at the gate, being generally annoying or using electrical devices. All those situations use different levels of energy and O2 which I refuse to split on my next flight.

Any restaurant that were to use the "charge them for everything" mantra of that shining customer service beacon known as the airline industry would have a very short flight indeed.