How close are you to the bride/groom?
Family? Friend?
Most of the time, if you underdress no one will say shit to you, but don't think it went unnoticed.
Mostly, if you go underdressed, you will make yourself look bad. ie jeans and runners.
How would you feel if someone came to your wedding wearing jeans and runners?
And what is it with you and sweaters over a button shirt? Are you Zach Morris? Just go with a clean pressed pair of slacks and a clean pressed shirt. A nice pair of shoes and you are good to go, at the bare minimum.
Hell, if you dress GQ enough, maybe you will score yourself a brides maid or something.
