Your example is the exact opposite of 'pulling it off'. If you see a guy wearing a huge watch, if he's not in the least bit self-concious over it, it'll look natural. I used to dye my hair back in my youth and I had scarlet hair at one point. Once I got used to it, it stopped being that unusual and nobody really took much notice of it. However, one Christmas, some bloke in our office decided to dye his hair blue for charity and no matter how he tried, he could never carry it off. Also, imagine your mum wearing the same clothes as Britney Spears ... no, on second thoughts, stop imagining that.
Some guy in a wet suit with a huge watch on isn't going to have his watch commented on. If he wears it afterwards, he won't think it's too big and therefore he'll pull it off.
ps. Nobody back in the 1950s could wear a Fiddy to work, unless their work was underwater, so it has nothing to do with body size and everything to do with fashion.