In all my years, the on-air giggles I've witnessed have only very rarely stemmed from something said or done by a pilot. On the rare occasion that they have been pilot-induced, it's been because the pilot said something to intentionally evoke said giggles.
For example, contrary to what you may think, we're not going to laugh at multiple failures in attempting to read back a clearance, because those attempts tend to eat up time we should be spending moving other aircraft.
On the other hand, you would have heard me unsuccessfully trying to stifle laughter on frequency that afternoon in 1985 when controller Ken, working a different position/freq next to me, told a helicopter to "circumcise the airport to the south...."
Dave