The "well-to-do" customer apparently wasn't interested in banking when he walked into the branch in Andovers around lunchtime on Friday.
Customer Gareth McCarthy saw the determined dumper.
"He didn't say anything at all, but you can tell from his face he looked angry," McCarthy said, according to the Daily Star. "I wasn't really paying attention until I noticed a foul, but unmistakable smell. I looked at the guy and he was just calmly walking around the bank -- going to all the areas he could."
The man also purposefully pooped on the bank stairs.
"It's quite clear what he was doing -- he just had this calm but angry look on his face, as he walked around leaving special deposits on the floor," McCarthy said. "And then as calmly as he walked in. he left. Staff didn't know what on earth had just happened. The stench was unreal."
On our newslist today - Barclays customers were shocked when a man walked in and did a POO on the floor of the bank. pic.twitter.com/jfJ6Gbg9w7— Jon Mills (@jonmillsphoto) June 30, 2014
The branch closed down while bank employees cleaned up the mess.
"I have no idea who that guy is, and why he covered the bank in excrement, but he didn't look ill – he just looked a bit smug as he walked out," McCarthy said.