Help on waistcoat

[PiobBear]

Well if it's semi-formal, it really doesn't matter, does it? It's your choice.

Yes, it bloody well does matter, and no, it isn't his choice; it's his hosts!

"Semi formal" is a dark business suit (not a blazer or sport coat), white shirt & tie, or kilt (a kilt, not a UK or something) and black (not tweed) Argyll with a white shirt & tie, with all the proper accoutrements (kilt hose, leather sporran, etc.). Highland or sassenach, it always involves a coat.

As Steve said, a waistcoat alone is not semi formal. If the invitation states semi formal and you don't have the proper kit, go in a business suit; to do otherwise is an insult to your host. The only time I wear waistcoats are with jackets, and then I leave the bottom button unbuttoned.