It was really best for everyone involved that he never saw her in the dress. True, they had eloped, so for all Tony knew, Pepper had not been a traditional bride. And okay, he was a little offended that they told him about their marriage after they'd already done it, without bothering to invite him to the wedding. He had tried to be distant with them--didn't want to be in the way--so if they assumed he wouldn't want to be there, it was his own fault.
He was sure he would have made a jackass of himself anyway.