Adventures of a Private Eye (1977)
[Detective Judd Blake has just caught his assistant peeping at the keyhole.]
Judd Blake: Amateur. Peering through keyholes is for the amateur.
Bob: I wasn't, actually, Mr. Blake. I just thought I'd dropped something on the floor.
Judd Blake: Bugging, now that's the professional way.
Judd Blake: Yes, and like everything else, purely a matter of technique. Now you stick with me, and you'll soon learn to be a successful bugger.