Well, you say are a dude and so, I’m not exactly sure. But if you don’t mind a little humor (even if it’s very, very little), one thing you might want to be sure to wear are … pants.
You know, this is real good advice. No matter how badly things may turn out, if she’s the one who chose the clothes (I’m not trying to be funny anymore. I swear I’m not), she can never give you any grief about it.
Yeah it’s her event so ask her how formally you should be dressed. If she says she doesn’t care, but you actually do care, then find out where the reception is and report back.
But it’s unlikely that will be the case.
DANG, Cat - I had no idea you were so devious. Come to think of it, I had no idea that anybody was so devious.
Gee, I wonder if I ever got any wedding sex. Inadvertently, I mean.
Red, the more I think about it, the smarter it sounds to wear whatever Cat Whisperer likes.
My fiancée won’t let me wear that for our wedding.
I asked. Numerous time.
You know, all I ever wore was whatever came up in the rotation. I don’t think I got anything inadvertent.
I don’t know about the wedding sex, but I do know that going to a wedding with a boyfriend who wasn’t willing to commit to me was extremely depressing and no doubt contributed to me deciding to cut my losses with him.
That would probably be best. 
Don’t wear white.
Be prepared for your GF to start sighing wistfully, “Isn’t this a beautiful wedding?”
Or wearing the same dress…
Don’t worry about it. In the overall scheme of things a guy who is a last minute invite is noticed or cared about slightly less than the color of the mailbox outside. Be comfortable and stand as far out of the way as possible.
I have my birthday suit if that’s any help?
Exactly. Unless the invitation instructs differently, wear a suit. Button-down shirt, tie, shoes. And if you’re motivated enough to go out and buy a suit, please please please remove the label from the sleeve. It’s not supposed to remain there so everyone can see the brand you bought. It is to be removed upon purchase.
And if you’re not the type to normally wear a suit, wear one anyway. No, the tie won’t choke you. No, you really won’t be that uncomfortable. Yes, your GF will appreciate it.
Enjoy the wedding.
I love suits on men but you certainly don’t have to wear a suit if it is not that kind of wedding. But please, a dress shirt and a tie and slacks. Not jeans and a sloppy t-shirt.
It’s ok for men to wear white shirts to weddings. If you have to ask for advice on an Internet message board you probably shouldn`t wear any other white clothes to anything, let alone a wedding.
Just popping in to say, this thread gave me a Doper crush on Fuzzy Dunlop for being a dude who knows how to dress. Also props to Cat Whisperer - I like how you think :).
This is why every man needs a black suit. It can be worn to pretty much anything
Ditto on asking the GF, unless she’s a bit clueless on that sort of thing. The versatile thing to do would be to wear a nice suit and tie, but be prepared to leave the jacket (and possibly the tie) in your car if you get there and notice everyone else has dressed more casually.
I love weddings! Men look great in dress pants, a button down, possibly a tie depending on the time of the wedding and a blazer.
nth recommendation of a suit. Or that failing, white shirt, dress pants, tie. Unless you know for sure the wedding is deep in the Hippy Zone.
This. If it’s smart, you’ll be appropriately dressed, and if it’s casual, you can take off your jacket and tie, roll up your sleeves and fit right in. As a Brit, though, the idea of taking off your jacket before your tie makes me cringe slightly. Take off the tie first, otherwise you’ll look like you came to fix the photocopier. Especially if you’re wearing a short sleeved shirt (represses another shudder).