What caused Nikita Khrushchev to refuse to attend the peace summit in Paris in 1960?

The downing of a U-2 spy plane by the Soviet Union

On May 1, 1960, the Soviets shot down a CIA spy plane and captured the pilot. Khrushchev flipped out at the Summit meeting on May 16th, accusing Eisenhower of spying on Russia (which we were) and stated that Eisenhower was no longer welcome to Russia due to his "i nadmissible, provocative actions" and basically humiliated Eisenhower publicly. Khrushchev stormed out like a crybaby and the next day the meeting officially adjourned, with neither Khrushchev or Eisenhower attending.