Would I be offended to see cake-smashing? No, but I'd be disappointed to be shown that any of my friends had such a coarse sense of appropriate fun for a serious occasion, an occasion at which formal dress is required. If smashing fits the occasion, perhaps afterward we should put on the television and watch "Lizard Lick Towing", maybe get everyone to sing "99 Bottles of Beer On the Wall".
I feel the same way about garter-removal ... maybe it fits in its basic form, but when you have a rowdy DJ/MC insisting that the bride push the garter waaaaaay up and then have the groom remove it with his teeth, well...
I still look back with a few regrets at my own wedding day. I couldn't tell my bride "no" about anything and make it stick ("but it's a tradition, everybody expects it" was, apparently, irrefutable logic). FFIL expected not only a dollar dance, but the obligatory downing of hard-liquor shots by participants (of which there were about three, all of them her relatives). She never had heard tell of anyone objecting to their car being "decorated" (by her brothers, of course), but I was able to get that single offense off the table.
If the whole-gosh-darned-please-let-it-be-over-soon event is solemn enough to make my wife believe an invitation equals a royal command to attend, then drop the boorish behavior. At least, that's my feeling.