[Tical]

I looked into this exact issue not too long ago.

Brunson advocates this play in SS2 to get a read on opponents in ring games. From the responses I got, if its not outright illegal in tournaments, its very poor form.

The last time I pulled this move my brother thought I was folding without saying so, and exposed his losing hand. As he was a beginner, other players (friends) got on my case for doing this, and I think they had good reason. It can be a confusing and devious play.