Quickest way to slip up doing undercover work is by doing things that you normally wouldn't do.
6 seconds sound clip from the Kindergarten Cop (1990) movie soundboard.
You can hear this line at 01:02:23 in the Blu-ray version of the movie.
Quote context
[...]
- Oh. Well, I got a bottle of wine for your big date...
- Oh, it's not a date, I know.
- But we don't want Joyce to think that, do we?
- Thanks. I don't think it's a good idea.
- Why not?
- Quickest way to slip up doing undercover work is by doing things that you normally wouldn't do.
- And flowers as well. Here you go. She'll love them.
- Wow. This is quite a place. They must be paying you a lot more than they're paying me.
[...]