For all the billions of dollars that flooded campaign 2012, the big tent parties celebrated the hard work of their faithful Tuesday night by charging them for drinks.

It seems the one thing both parties can agree on is not paying for booze. To be fair, donors got drink tickets, so it wasn’t entirely cash bar.

Still, this has set etiquette experts on alert.

“You know, we’re not blanket against [cash bars],” says Anna Post, author, spokeswoman for the Emily Post Institute and great-great granddaughter of Emily Post herself. “However, you can’t invite someone to dinner and then expect them to pay.”

She does say that if one must have a cash bar, then one must tell guests well in advance, such as on the invitation or event website. Guests have to understand that this is the deal before they get there.

It’s not so much about guests getting toasted on the party dime. It’s that an open bar is about tact.

Nevertheless, the cash bar didn’t deter the political parties from partying.

At the Democrats’ party at the Liaison Capitol Hill — where Diet Coke went for $6 a pop — party-goers got smashed pretty early. One tipster said she was almost knocked over by the smell of vomit in the bathroom.

“It was the grossest thing I’ve ever seen,” the tipster said. “Well, since college.”

There were no reports of drunk and disorderly behavior at the Republicans’ party at the Ronald Reagan Building — but most people cleared out before 10:30 p.m., having little to celebrate.

Post puts it this way: “My take [on cash bars] is always that the most gracious thing that you can do is ‘host’ your guests. It’s the spirit of inviting someone in the traditional hosting sense,” she says.

“I’d have to do some research,” she continues. “But, I’d be willing to bet Emily Post never went to an event with a cash bar.”

Post recently completed “Emily Post Etiquette, 18th Edition.” We suggest everyone read it before inauguration season.