We're pretty informal when it comes to mussels, and our personal preference is scooping up a bit of the cooking broth and then slurping the mussel straight from its shell. This is honestly one of the most sensual and perfect eating experiences we can think of, and we find it satisfying in a way that goes way beyond simply filling our bellies.
That said, there are definitely some situations where this would be considered uncouth. Eating with in-laws or at a nice restaurant come to mind! In these situations, we opt for holding the shell in the fingers of one hand and using a fork to scoop out the meat. We lose our beloved pan juices, but it's definitely a neater way to eat.
Using an empty shell as a tweezer to pick out the mussel meat never occurred to us until we did a little research for this post. This strikes us a perfect compromise between slurping and using a fork, and we'll give it a try next time we have mussels.
And anyway you go, we think mopping up the leftover cooking broth with a little bread is a must. You just can't let that go to waste, proper etiquette or not!
Related: How to Clean and Debeard Mussels