I can't stand the smell of coffee. Well, can't stand is probably a little harsh, but let's say I find it nasty smelling. I don't know why anyone would pour something as foul as coffee over their taste buds.
But that's not what this is about.
I just find it in bad form for a teacher to do a recess, cafeteria, or a dismissal duty while also sipping a beverage - coffee or otherwise - from a cup in hand. First, did you bring enough for everyone? Second, how dependent are you on the drink really? And third, can you fully devote yourself to your duty, which often requires two hands.
It just something to consider.