It wouldn't be difficult, for example:-
(1) You could give a VMC-only aircraft (or non IMC/IR rated pilot) a steer that takes it right through a bank of cloud, which is likely to be invisible to you on radar.
(2) You could ask a Piper Cub to take a route over a town that complies with the 1500ft rule, but not be aware that, unlike the last one you handled, which was on a CofA, that particular cub is on a permit and therefore not permitted to overfly built up areas under any circumstances.
(3) You could clear a Shadow onto finals at Shoreham on runway 25. But, because this is a microlight Shadow, not a group A Streak shadow, it isn't (until the rules change later this year) permitted to overfly the adjoining conurbation even on finals to a licensed aerodrome.
All of which would be instructions given by you in good faith and applying your best level of professionalism, but where the pilot if he is doing the same would be REQUIRED to decline the instruction and ask for an alternative.
G
N.B. SSD, please feel free to carve and reproduce it anywhere you like, with my blessing.