going cowboy

Going against the rules or set of norms. Breaking the mold, usually in a spirited or rebellious manner. Similar to "going rogue". Often times reckless or careless in their pursuits.

"Why do we have so many office supplies? 2000 red pens? 500 boxes of staples? We only have 10 employees!"
"Bob from accounting must be going cowboy with the credit card again."