OK, this is in Not TA, but lets start with a couple (ha!) of examples from that very source. It’s ‘Adam and Ian’ and Brian and Jennifer’, never the other way about. And to take some from my own store, it’s ‘Maria and Andy’ and ‘Lynn and John’, but ‘Peter and Mary’ and ‘Brendan and Helen’. And the thing is, everyone else uses that order too. It’s not just partnerships, either: the same thing with siblings: ‘Carol and Helen’, ‘Simon and Helen’, ‘Tony and Peter’, ‘Declan and Ger’.
What determines it? Is it euphony? And if so, how is it working?
Oooh, what a lot of Helens. Only one of the three mentioned is certifiably bonkers, but oh boy does she make up for the other two.