What would you do if you were in the bride's place or just witnessing it?

Laugh it off and let it go.

I would have been embarrassed and angry no matter who was responsible for the insulting situation.  When he's walking down the aisle to stand before the congregation everyone sees the bottom of his shoes and it turns into a bad joke.  I would have asked him to change shoes and demanded an apology.

The odds that this would have upset me at my wedding are zero.  In fact, I think it's pretty funny.  Be careful what you read and believe with online comments.  On the internet, there's lots of bored young teens who are legit trying to be helpful, but they're clueless.  Any bride who gets upset over something like this is tapping into a doubt or concern she has about her groom.

I not only have a sense of humor but this wouldn't even be an issue for me because there's no kneeling at a Jewish wedding so no one would even seen the soles of the groom's shoes. 

The problem with sensitive people is that they are often up-tight and have issues with recognizing humor.

I would have laughed it off as a funny joke. Because the reality is, the groom had the freewill to walkaway... but he didn't. Whether he knew about what was written on his Shoes, or not, is relevant to the overall joke of the matter.

The priest who married us kept calling the groom the wrong name. I married a guy named Robert, apparently. Was I upset, Noooo...it was funny!

sounds like you can't take a joke, sensitive or not.

If you think your guy would intentionally do this knowing it would hurt you, I would wonder why you were dating him let alone marrying him.

I would hope I'd know my intended's character well enough to know that he/she wouldn't countenance making a coarse jest of something so serious and beautiful as marriage vows. If I learned that I was very wrong about his/her character then I couldn't possibly overlook that. No marriage vows would happen. 

Why make an issue of it? This isn't a new 'prank', and it's entirely possible the groom wasn't aware. I wouldn't see the point of letting it spoil the day, or your first night as a married couple, when there should be so many better things to consider / remember.