I'm typically not a real fan of giving clothing as gifts - and neckties count. Especially if it's not to someone you know really, really well (like, a parent/child, a spouse, or a sibling). Since you don't know the fellow's neck size, I'm guessing he's not your parent or child, your spouse, or your sibling, since in any of these cases finding out his neck size would be pretty easy. And I'm even less of a fan of giving unusually large clothing as a gift. It's just got too much potential to go badly. So please reconsider your proposed gift. (Although it could be worse, I suppose. The recipient could work at Chase.)
Thanks for the advice. It's for a wedding/groomsman. I'd rather get him something that looks good on him instead of getting the same ties for everyone.