That's gonna stink
By stating: 'That's gonna stink', a person has playfully, but politely notified those persons within ear shot that a he/she has just passed gas and that the purveyor of said fart believes it will produce foul odors. This statement can be applied to loud, distinct flatulent expressions as well as those of more subtle qualities.
'That's gonna stink' said Emil having passed gas just as he was exiting the elevator, leaving those unfortunate passengers continuing their journey within its confined space to fend for themselves.