Got a reddener in Brussels a few years ago when I asked for a Kwak, and overheard the bar men while they rummaged around under the bar looking for the "verre tourist".
I heard somewhere that it was originally a type of glass used by stagecoachmen - I guess a olden-day cup holder.
I was passing the B&C last night, 50/50 about going in becuase it was getting late. In the event, I was deflected by very loud music. Just not my thing, I'm afraid. Does that happen every night?