Respected X-Markers

[MacMillan of Rathdown]

Anne has (as is usually the case) made all of the salient points. To which I would add:

1) Trust your tailor. He has probably made dinner suits before.
2) All of my tuxedos have back pockets-- only my evening suits (tails) are made without back pockets.
3) All of my tuxedos have a double vent in the back-- I find it makes the jacket much more comfortable when seated.
4) Coloured pocket squares are for day wear. Formal attire requires a white pocket square (with a spare hankie tucked into your back pocket).
5) Cummerbunds are optional; a three button waistcoat being equally appropriate (and in any colour one may fancy).
6) All of my formal jackets have a functioning button hole in the left lapel. (Here I am going to slightly disagree with Anne [sorry Anne] about boutonnieres: Unless one is a poncy Belgian private eye, with a name like "Hercules Porridge", a gentleman does not wear one of those little silver vases pinned to his lapel. He threads the stem of the flower through the button hole, and fastens it on the back of the lapel with either a pin, or it passes through a loop of thread (called a becket) or under a bit of tape, which holds it in place.)
7) Buttons on the sleeve should be functional, but it is considered poor taste to leave them un-buttoned (a gentleman doesn't show off).
8) A fold over collar is a better choice than a wing collar. With a wing collar the tie will ride up over the collar, something that won't happen with a fold over collar. It will also be more comfortable for someone not accustomed to wearing a heavily starched collar.
9) Shirt fronts are a matter of personal taste. I prefer a narrow pleated front with small black studs (black tie) and a stiff bosomed shirt with small gold studs (white tie).
10) Formal dress trousers are never cuffed; those worn with a dinner jacket have a single satin stripe (about 7/8 inch wide) over the outside seam. Those worn with tails have two narrow satin stripes (about 3/8 inch wide) on either side of the trouser seam.

And as an aside-- kids, especially at their first Prom can be really, really, rough on their clothes. Are you sure you wouldn't rather hire them for the evening?