Suspenders are considered underwear and are not meant to be seen by anyone.
Perhaps by 16 people, worldwide, assuming we are writing in the year 2010 and not 1890. I can say with great confidence that people have been showing suspenders with impunity for at least 30 years, if not 100.
In any event, this is entirely beside the point unless there's some reason to believe that people wearing cummerbunds take their jackets off more often than people wearing vests. Typically, you can see the suspenders under either. They look slightly (but only slightly) funny under a vest, and not funny at all under a cummerbund.
This is one of the primary reasons that you never remove your jacket at a formal event.
People do, in fact, remove their jackets at formal events. In any event, the word "reason" here defies understanding, considering (a) people often wear suspenders at non-formal events and (b) the whole thrust of your post seems to be toward telling people
not to wear suspenders at formal events. I'm not sure I follow why the primary reason for not removing a jacket at a formal event is to avoid showing suspenders that aren't necessarily there, as opposed to removing a jacket at work, when they very well may be.
the cummerbund is the informal of the two pieces and it is to be worn with a shawl collar jacket, while the waistcoat is to be worn with a peak lapeled jacket.
You can cheerfully wear them in any of the four possible combinations.
Whether you prefer to wear calf leather as opposed to patent leather is not the point, it's still not appropriate or conforming to the formal dress, or in this case, semi-formal evening dress code.
I will pass that on to the 98% of people who don't wear patent leather shoes to formal events, as well as the remaining 2%, almost all of whom got their patent leather shoes in a set together with their rented tuxedo and pre-tied bow-tie.
