"Guinness: it turns yer shoite black."
-Christy Moore

Let's talk about a pint of the black stuff.

Guinness

Many of you namby-pamby nancy-boys with undescended testicles are afraid of Guinness. "Oooh," you say, "It's too thick." Well, your Mom's too thick, and that didn't shtop me lasht night, Trebek.
The truth is, Guinness has fewer calories than a glass of skim milk. Sure, the roasted flavour takes a bit of getting used to, but it's no more bitter than coffee, although not that frappe' nonsense with more sugar than a bowl of kellog's frosted sugar lumps.

Guinness is a style of beer known as a dry Irish stout. This means that it contains barley, hops, water and yeast, just like any other beer, but a portion of the barley is roasted to add flavour and colour. Arthur Guinness is often thought to have coined the term "stout" when he started brewing at St. James's Gate in Dublin. This, as they would say in Ireland, is a load of bollix. However, he is one of the first proponents of the style, which is a derivative of porter.
Initially, Guinness was quite a strong beer, in the 7 to 8% ABV range. Nowadays though, it's a quaffable 4.3. This is because Guinness is owned by a giant soulless multinational corporation, who sucks.
There's quite a bit of cultivated mystery surrounding Guinness and how to properly serve it and so forth, and most of it is sheer unmitigated nonsense. The whole two-pour system was originally from the cask serve days when flat beer was poured into 3/4ths of the glass, and then topped up with fizzy beer when ordered. There's no need for it today, and it doesn't taste better the closer you get to St. James Gate. I had a pint of Guinness in Derry that was twice as good as the one I had in Temple Bar, and really the only difference between them was that Dublin was full of drunk Germans, who ruin everything.
Incidentally, all Guinness uses isinglass from processed fish bladders to aid in filtration. So you can forget about bloody water purity.
The Wolf and Hound in Vancouver will make you a few Guinness mixed-drinks, and they're quite good. You can also cook with Guinness, and it pairs nicely with rich meats like lamb, and sharp cheeses. If you can find it served extra cold, and you purchase it, may a thousand vengeful leprechauns rip out your liver and use it as a trampoline. Guinness should be drunk, like any stout, moderately cool.