**Spoiler Alert**
In the third chapter (exhale) after initially meeting Rob in the dining car you will again meet him in one of the train cabins (after an interesting phone call). During your conversation he will block you from exiting the train car, after trying to reason with him he won't budge so you are left needing to utilise an item in you inventory to see if you can get out. There is an obvious choice...
The not so obvious choice however is to pump your asthma inhaler in his face... which is exactly what you need to do to pop this achievement! Simply move you mouse to the top of the screen to access your inventory, left click on the asthma inhaler and then left click on Rob... job done.