hardass syndrome
a puny guy who works out a couple times and suddenly thinks he's a hardass, and thinks he can keep up with the big dogs, and that he's invincible. Synonyms - small dick complex, badass fever, wannabe Brian Cushing
Look's like that Steve kid has a serious case of hardass syndrome. He's only 120 pounds but thinks he's as strong as a linebacker because he lifts weights two times a week.