The "Bro Code" might've gotten a lot of publicity from NPH on How I Met Your Mother, but dudes have been claiming the existence of "man rules" for as long as there have been dudes -- or rules, for that matter.
Yes, the list of "thou shalt nots" for guys is very real, and while there's no universally accepted codex of bro-dom handed down by ancient scribes, a recent AskReddit thread has neatly encapsulated many of these unwritten (yet still frequently written, somehow) rules. Here are the best ones, which none but the most dastardly of scoundrels would dare disagree with:
The Duty of Riding Shotgun
In for a Penny, in for a Pound
Your Favorite Beer Brand Is "Free"