Another thing to consider: nicotine accelerates caffeine metabolism. Therefore, if you are feeling irritable and have recently ingested caffeine (coffee, tea, energy drink, etc.) then you can expect a craving for the antidote.
Think of all those folks who used to hang out at coffee shops, smoking cigarets. Up on the cup of coffee, down on the smoke. Just riding the roller-coaster all day.
Also important to cut out caffeine if you are stopping nicotine. And understand that caffeine can be a trigger, nicotine accelerate caffeine metabolism (cuts the edge) which is why the coffee-drinking cigarette smoking trope exists. Caff and Nick are the best of friends.