Advice: What to Do When Seatmate Is Overweight?

The problem of over sized passengers taking up the space of passengers sitting next to them is becoming rampant! Gate agents and in flight staff are afraid to confront over size passengers when it is obvious that they are flowing over to passengers seated next to them. On a recent domestic flight I was in a economy comfort window seat and an oversized passenger sat in the middle seta. This passenger was so large that I was pinned to the window and had to sit sideway on a 1 hour flight. The passenger on the aisle had to sit with half his torso spilling over to the aisle. The flight was full and boarding was just about over when the over sized passenger made their way to the seat. The passenger was well aware that she was taking up my space. I have complained to a major airline and get back messages that are vague and do not focus on a decent answer. Airlines are putting in smaller seats and this has caused part fo the problem. Many airlines have containers by the departure gates that one has to put in their crayon and if the bag does not fit, it has to be checked. Yet over sized passengers have free access to sit in seats to small for them and inconvenience the passengers sitting next to them. Over size passengers need to either purchase 2 coach seats or buy a larger first class seat. Gate agents and in flight staff need to be more attnetive in trying to elevate this situations. Major air carriers need to step up to this issue which is getting worse then ever.