Onterrio Smith
Technically this isn’t a mistake because Smith knew what he was doing. However, he didn’t intend for people to know that he carried a prosthetic urination device in his bag. The Whizzinator entered NFL folklore after he passed through an airport with dried urine and a mysterious appliance.
The NFL discovered that he was attempting to cheat the system. This had career-defining consequences because Smith was a known drug cheat. He served a one-year suspension but then he became damaged goods. Nobody wanted to sign the running back after his shenanigans (via CBC).