1) Walking out to the a/c for a GH trip with the intention of throwing in some aeros to find student sitting strapped in, engine running and checks complete with several kilos worth of Transair catalogue purchases piled unsecured in the back.
2) Students who decide they're going around on a PFL regardless of whether or not I reckon they're going to 'get in' to their chosen field...
3) Carefully briefing the student that their initial call for a zone transit to EDI Approach at 1700 on a Friday should be as brief as possible, followed by nod of understanding and then capped-off by them pressing the PTT and giving an epic 7 minute ramble of umms and errs interspersed with the details of every turning point on their 2 hour navex, what they ate for breakfast and the names of their pets, during which at least 2 IFR inbounds fly through the localiser. Desperately try to prise students thumb from PTT switch.
4) Despite repeated briefings on the perils of going IMC as a student, sitting on a nav trip as your student manages without fail to find a solitary cloud, penetrate it, and then after a 10 second delay ask what they should do now...
And more Trial Flight gems...
"Is this your plane?"
"Do you have a proper job?"
"Is this your hobby?"
"Where's the clutch?"
"We don't seem to be moving" (at 3000' doing 90 kts)
"Are those clouds?" (I really was asked that once...)
And as has already been mentioned, make sure you give no warning whatsoever before honking your lunch over the instrument panel and my left arm.
And finally... I once had the mother of a 14 year-old boy write a letter of complaint to the flying school because I had not allowed her son to land the a/c unassisted on a trial lesson even though 'he'd done it on his computer at home'.
Still enjoy instructing after 4 years of it though
ST