Your oxygen mask only holds 15 minutes of air. The bathroom door you just locked is an illusion. And there is a reason the crew secretly refuses to drink the onboard coffee.
1. The lavatory lock can be bypassed from the outside.
Flight attendants can easily unlock lavatory doors from the outside. There is a small latch hidden underneath the "Lavatory" or "Occupied" sign on the exterior of the door. This is a critical safety feature in case a passenger experiences a medical emergency inside, but it also allows the crew to intervene if someone is smoking or refusing to return to their seat during landing.
2. The coffee and tea water comes from rarely cleaned tanks.
The coffee and tea are made with water from the plane's internal tanks. These tanks are notoriously difficult to clean and are serviced infrequently. Environmental Protection Agency (EPA) studies have occasionally found coliform bacteria in aircraft water supplies. While the water is heated to brew coffee or tea, many flight attendants bring their own bottled water and avoid drinking the brewed beverages on board.
3. The oxygen masks only provide 12 to 15 minutes of air.
If the cabin loses pressure, the chemical oxygen generators deploy and provide a steady flow of oxygen for only 12 to 15 minutes. This is not a design flaw. It provides exactly the amount of time a pilot needs to initiate a controlled descent and bring the aircraft down to a safe, breathable altitude—usually around 10,000 feet—where supplemental oxygen is no longer required.
4. The chimes are a coded language.
The chimes you hear throughout the flight are not random. A single chime often means a passenger has pressed their call button or the seatbelt sign has been toggled. Two chimes indicate a call from one crew member to another, or a warning that the plane is approaching 10,000 feet. Three or more chimes in rapid succession signal severe turbulence, a warning from the flight deck, or an emergency.
5. The cabin lights aren't dimmed so you can sleep.
The reason the cabin lights are dimmed during nighttime takeoffs and landings has nothing to do with sleep. It is a safety precaution to allow passengers' eyes to adjust to the dark. If an emergency evacuation is necessary, passengers need to be able to see the floor-level escape path lighting immediately, rather than waiting for their eyes to dilate after being blinded by bright overhead cabin lights.