Originally Posted by Merkaba

But it's like hookers says, you are only shouting a round out of your own kindness. Perhaps one shouldn't shout a round until they're fairly certain they're in the company of people who you know will shout a round back.

It's not an obligation to return the favour, but it is polite. I guess someone shouting a round of drinks is the equivalent of second base.

An open tab would be like a homerun