@Vree  
Sometimes it works

she’s a fraud, but i wouldn’t like her as much if she wasn’t.

In Japan it’s supposed to be good manners to slurp. Maybe that’ll stick in the dub version?

@sirvancelot  
Yeah. Allegedly, slurping evenly distributes the drink across your palate.

You’re actually supposed to slurp when drinking expensive teas or coffees. It engages more taste buds and your sense of smell than simply drinking.

@TheAbridgenator  
Pretty much. Although some people seem to like the burn, judging by how hot they drink their tea. I’m on the absolute opposite of that, though.

@Knox  
You HAVE to slurp when you drink tea. Nobody likes burned tongue.

Maybe slurping isn’t rude in their culture.  
(Also, Rarity is obviously a social climber, look at her parents.)

That’s cartoons for you.
 
Do you really want toons to act stoical and reserved?

I’m just surprised she doesn’t magically create a pinky to raise.

Meh, I slurped when I used to drink tea.

Nopony’s perfect.

A little slurp isn’t bad; a tinge of imperfection heightens perfection. (Also, consider her apparent upbringing environment. She’s doing pretty dang good for herself if the most notable lack of manners is a little sip.)
 
A nerve-wracking, 48-ounces-and-I’m-already-hitting-bottom, my-straw-is-a-gateway-and-my-mouth-a-black-hole gurgling SSSHLORP, on the other hand, is entirely out of the question for one of such refined state.
 
(That’s left to Pinkie, who will subsequently have no idea why Rarity is staring with a combination of disgust, shock, and a tinge of awe.)

slurping is fine if you do not do it loudly in someones ear xD

Slurping is an artform.  
You need the perfect balance of volume and duration.

SHUTUPRARITYSACLASSYFINEASSLADY
 
Also, tis fine to slurp so long as you don’t make a show of it. Like drinking from a bowl, or watering down the good scotch so your friend doesn’t notice you sniped some!

But she’s a horse.

Why the greentext?

Celestia herself does that.