If the UN had teeth, it would embargo America for being complete assholes to its neighbours.

The UN is structured to reconcile global powers and avert a third World War. To that end, the big players on the National Security Council effectively hold one another in check (unless they fuck up and abdicate their roles, as when Russia boycotted the vote that kicked off the Korean War). It isn't that the UN lacks teeth. It is that these teeth are for biting weaker third world nations, not members of the organization's own inner circle.

Is it time for the members of the UN to rebel and throw out the ruling founder class?

That would defeat the fundamental purpose of the organization. The goal is to establish open channels of communication between sovereign states, not to pick sides in transnational disputes.

Now... if the BRICS wanted to render aid to Venezuela as part of a pact of common defense (not unlike NATO or Warsaw during the Cold War Era) that would make a lot of sense. China or Brazil doing an Operation Cyclone out of the Tepui Mountains would be ironic in its own way.

But I doubt the Americans are really interested in that kind of fight. We seem to have settled on "Send a few B-2 bombers to wreck their historical sites and academic institutions, then demand a token concession to prove you're our bitch" as operative American military strategy.