Pre-flight Safety Demonstrations
At the start of every flight, you get a brief briefing (I know, bad writing, right?) of all the safety instructions on the plane; this includes how to use the seatbelt. I'm dumbfounded why this is still the case. Yes, passenger don't know how to use their seatbelt which has only two movable parts, the strap and the unlocking mechanics. Why not have a mandatory briefing when you enter a car because car seatbelts are definitely more complicated?

When will we be able to stop broadcasting the fact that people cannot smoke on airplanes...? Restaurants don't even have to inform their customers with any signage!
One of the best parts of the briefing is seeing how the flight attendant goes about demonstrating the oxygen mask. Some attendants show where the masks drops, others reenact the masks being dropped from overhead. The climax of the briefing is how they show how to use the masks. Knowing that the mask has been used over and over for every flight, most are hesitant to put the mask anywhere near their face (almost treating them like a sick person). I've only have seen one flight attendant who actually put it on his face. And remember, the plastic bag may not inflate.
The most annoying part about the pre-flight briefing? Well, the guilt of not really paying attention to the flight attendant is high up on the list. Poor flight attendant, they're basically the Terms and Conditions that almost no one reads. But the worst aspect of the entire briefing is trying to figure out if the use of "lighted" is more correct than "lit".