Size-mismatched PC and vest—what to do?

[McMurdo]

Is the Burns night you are going to Black Tie? Do you have another jacket to wear? If not, then by all means wear the Prince Charlie jacket without a waistcoat, it has been done before. If it's not black tie then wear an Argyll jacket if you have one, if not perhaps a shirt with a jumper over it, this keeps the outfit casual but still works for many events when not going black tie.