I came across this interview tonight. It's from 6.21.12.
This is the most uncomfortable but also amazing late-night interview I've ever seen. Letterman destroys Justin Bieber with daggers in his eyes. He mocks him, makes fun of him, talks down to him, backs him into corners. It's filled with awkward silences and semi-heated exchanges. Letterman gets pretty mean at times too. Bieber is like a sheep to the slaughter.
Check it out: http://www.youtube.com/watch?v=Z4T4__HyeXE