Crowley is either walking to or from one of those bars (who knows) and catches a glimpse of Shen Qingqiu in the lounge through the open door. Great. He's going to tattle on Crowley to Aziraphale as well and then Aziraphale's going to use the word reefer again. Might as well try and balance it out a little.

"Hey," Crowley says, poking his head in the door - and he says this very solemnly and importantly, "make sure to enjoy it responsibly."

And then he's off.