Are you suggesting that airport screeners do this? That they put unknown substances on their gums? I'm surprised you don't suggest they snort it or inject it to test for purity.
But let's play your silly game and say the airport screeners tested this way. You're going through security carrying your flour-filled condoms which you always do (hey, it's not a crime!). A screener tests it by rubbing some on his gums (the official Nate505 Airport Screener Drug Testing Procedure #B56a) and states that it was numbing and you're under arrest.
That's it? You're going to accept that?!
You're a funny guy.
No, I'm not suggesting airport screeners do that. I would suggest the cops do that. But if they don't want to for safety concerns, you can easily look at coke and flour and see the visible difference between the two. Coke has a much finer consistancy, like baking powder. I'd also insist they test it with their kit about three times. Apparently, the cops and their testing procedures failed big time in this case.