Some establishments (used to, anyway) give a button or wristband to a DD to ensure they got all the free soft drinks (and sometimes appetizers) they wanted, but others couldn't abuse it.
As far as being the DD for a group, I'd insist on driving one of their cars. Puke problem solved.
As far as being the DD for a group, I'd insist on driving one of their cars. Puke problem solved.