I once, in Ireland, threw a teen movie themed party. The red cups were key to it. I had to order them on eBay but they were weren't real Solo cups, just cardboard. They still went down a treat! Eventually somebody capitalised on the novelty and started importing them.

My experience with the Irish from the early 00's, is that they thought those red party cups are the most horrible thing ever, and they thought it funny that we use them. If the people I met ever used them, it was with irony. In the late 90's German business guys thought that Breath Savers were just like phenolic cakes from urinals and thought it was hilarious to feed them to their American coworkers. I get the same vibe from both situations.

In the UK I saw red Solo cups for sale labeled "Red American party cups"

Proper beer pong cups should be the smaller translucent Solo cups. They offer a smaller target and a better view of the carnage with violent dunks or pass-though cup splits. (My co-ed house had a very dynamic set of rules for Beer Pong. Ultra-low net, super fast serves, twitch reflexes, hyper environmental play, thrown paddles. You haven't played real Beer Pong until you've played our house rules from the late 80's.)

I come from Canada, and I was shocked

That's odd, because we've had them for quite some time (and played beer pong with them). </Ontarian>

Growing up in Alberta, the Red Solo Cup has also been a staple of every house party I've ever been to.

McMaster university. Never saw beer pong. Or the ubiquity of the solo cup (sure there are red cups in Canada, but in the us they are everywhere)

Red Solo cups are too expensive to play pong with. Pong, (at least played properly, none of this ball tossing nonsense), is very cup-intensive. Some of the more interesting variations require upwards of 100 cups to lay out. And you don't tend to reuse cups, unless you are really desperate.

$152 https://www.amazon.com/SLOP16RLRCT-Solo-Plastic-Party-Cold/d...

$25 https://www.amazon.com/oz-Plastic-Cups-Bulk-Packs/dp/B0098MR...

Costco is your friend. Also, you can put Solo cups in the dishwasher to extend their use a few times.

http://www.costco.com/Solo-Party-Plastic-Cold-Drink-Cups-16o...