Density altitude, I know that gal well.
Flew in to Jamestwon for a Fathers Day fly in. Had a 150D Cesssner! And a rather large girlfriend, and my big self. I chose to leave rather late in the day on Sunday, just to let the air cool a bit. Took off with the first notch of flaps, 15 deg? Heading to the West on take off the runway dips down a bit, lifted off just at the end of the runway, got 100 extra feet, and that my friends was it, all the way to LVK, not one more foot. I sure was glad I waited them extra hours.
You gotta respect that heat!
*BTW, I have seen planes land wheels up. The way he was waffeling around down low, I agree with Flyboy, I think he forgot to look for green lights!