It's happened loads of times. One I remember was at Wattisham in about 1982/3. A Hawk (100 Sqn or were they still Canberras then?) took up a Fighter Controller from Neatishead for a bit of DACT with the resident 56 Sqn.
FC said afterwards that he never touched
anything and couldn't explain why he decided to make an unplanned exit over the southern North Sea! Meanwhile said Hawk landed back with a "pole" poking out of the rear cockpit.....
Another well-documented example was a "cabriolet" F14 that was written up in the USN's "Approach" magazine with some rather spectacular air-to-air pictures. With such a big canopy completely missing the cockpit must have been extremely draughty....
A picture tells a 1,000 words....
When flying with a non-aircrew pax don't bank more than about 130 degrees and avoid negative g.....instinctively they make a grap for the yellow & black "handle".
MB