Dean drinks his coffee black, straight up. Nothing fancy; just nice, and strong, and scolding hot. He's taken it that way for as long as he can remember; probably stems form a deep seated need to impress his dad. No other reason an eleven year old would force himself to drink something so bitter without sugar than to try and prove he can take it like a man to a drill sergeant of a father. It doesn't matter that John didn't notice, he still did it and hasn't changed his ways ever since.
Sam drinks low-fat hazelnut lattes, easy on the foam. A Preppy Latte, as Dean refers to it. Dean thinks his younger brother would drink decaf if he didn't rely so much on the caffeine to stay awake. John notices Sam's choice of coffee; can't help but not when Sam gets pissy at the fact that the waitresses in these backwards diners they eat at wouldn't know a latte if it spilt itself down their 38 D squeezed into 36 C fronts. That's when they're forced to stop off at Starbucks or something similar which John sees as nothing short of a waste of time and Dean sees as the perfect chance to raid the condiment stand. For someone who doesn't take sugar in his coffee, he has a rather large collection of sweetener sachets.
Then Sam leaves for college and everything changes.
The first time Dean goes to order coffee, he orders for the both of them without even thinking. He sits looking at the two Styrofoam cups perplexedly for several minutes when he's order comes before picking up the Preppy Latte and taking a sip. It's milky and tepid and tastes like crap and that's all before the aftertaste of the hazelnut syrup hits him and then he's trying not to hack up all over the place. He glances longingly at his own steaming cup of black but persists with the one in his hand and if he just sort of holds his breath and gulps it down. It's not the worse the thing in the world. It's not that bad. Then again, 'not that bad' doesn't hold much weight when you're a Winchester. 'Not that bad' as opposed to getting sliced and diced and shot at and burnt and cursed and possessed...'not that bad' really ain't that good.
Dean drinks Preppy Lattes for the next four years.
The first time Sam orders coffee after he's left all he's ever known behind, it's in a coffee house with a bunch of people from his orientation group. He's never seen so many different flavoured syrups in his life. Most of his companions order a three quarter shot-low-fat-soy-decaf-frappacinos or variations thereof. Sam himself hesitates at the counter as the pimply teenager at the register looks expectantly at him. He orders a black coffee. He has no idea what to answer in response to the question 'espresso or filtered?' and goes with filtered. After a sip of the strong, black, ohmygodHOT, liquid, he resists the urge to dump half a dozen sachets of Nutrisweet into it and endures the bitter taste, wishing it were cooler so he could just gulp it down.
Sam drinks black filter coffee for the next four years.
The first time they order coffee together again, Dean raises a quizzical eyebrow at Sam's choice. Sam's own eyebrows disappear even further into his bangs as Dean then proceeds to order a low-fat hazelnut latte, easy on the foam. Their drinks arrive and they both stare stupidly at them for a moment before exchanging their respective Styrofoam cups without a word.
It's the best damn cup of coffee either of them have had for a long, long time and it has little to do with the taste and everything to do with the company.