"Fun" to watch the unknowing trying to fly a C172/PA28 IFR in the New Mexico mountains in summer. MEAs of 10,000' with temps at the surface near 100 f. Since it wasn't our place to try to talk sense into them on the radio before departure, we'd wait until they'd staggered up to near 7000' MSL, where they would have to cancel IFR, or return to land. Apparently, they slept through the chapter on density altitude.
Have also seen aircraft crash after departing a 9000' runway, and never get as high as the control tower cab before impact. (probably had it full rich too.)