In September, 1966, when Cream was rock's current supergroup, an up-and-coming guitarist boarded a Pan Am airliner from New York to London. One reason for the trip was a desire to meet his idol, Eric Clapton. Keep in mind that Clapton had become so popular that graffiti proclaiming "Clapton Is God" had popped up around London.
Hendrix's new manager, Chas Chandler (former Animals bass player) had promised a meeting with Clapton, which he fulfilled. There was a particular night when Cream allowed Jimi to join them for a jam at the Regent Street Polytechnic in central London. Then Hendrix unexpectedly asked if he could jam with Cream. Clapton, having never seen Hendrix live, said yes.
Hendrix Hendrix blew into a version of Howlin' Wolf's 'Killing Floor' at breakneck speed. Clapton, unable to keep up, dropped his guitar and walked off.
Keith Altham of New Musical Express recalls Chandler going backstage after Clapton left in the middle of the song. Clapton was furiously puffing on a cigarette and telling Chas: "You never told me he was that f—ing good!"
Altham said that just before he went on stage with Clapton he said, "I want to see if he is as good as he thinks I am." – which is not at all the remark you first think it is.
Here's the story as broadcasted by the BBC (Is that Max Headroom?!)