What is the big appeal of the Yeti cups?

Marketing, marketing, marketing.

Are they any better than other insulated cups? No. But they have a cool name that shows that you are one of the cool people. Kinda like having a D&B purse or a Trina Turk dress.

I don’t have one, but I can see the appeal: they are re-usable, portable, and good for either hot or cold.

A good functional hard working piece of equipment is always popular.

I’ve never seen that ‘brand’ here. However, we are encouraged to use non-disposable cups for our coffee. Often coffee shops will sell them at a quite cheap rate. You then just take it back in to be refilled rather than getting a takeaway, disposable cup. It’s a good idea I think. Your refill is cheaper than just buying a coffee with a disposable cup.

We got one for Christmas from my university. Everyone drinks coffee. Better we use a reusable cup and cut down on waste, it has the unis logo on it too.

Female bigfoot or manboobs?

As @rojo says, it’s all about the marketing.

Conspicuous consumption for the trendy.
$2 flea market find in 2 years.
Yawn. Pass.

Its actually stainless steel, so:
It’s not aluminum, which is known to have neurotoxic effects.
It’s not plastic, which is known to have endocrine-disrupting effects.
It’s not glass, which is heavy and breaks if it falls.

So it’s metal. Lightweight, inert, portable and reusable.