be one of the boys

To be an accepted member of a particular social group, especially one made up primarily or entirely of males (usually men, not boys). Primarily heard in US. John's a nice guy and all, but he's just not one of the boys. As a woman working in this industry, you have to be one of the boys while still being seen distinctly as a lady. You need to stop doing all this dumb, dangerous stuff just to prove you're one of the boys—it's not worth it.

be one of the ˈlads/ˈboys/ˈgirls

(informal) be a member of a group of friends of the same sex and a similar age, who meet regularly to enjoy themselves: His wife doesn’t understand that he likes being one of the lads from time to time. ♢ She’s never really been one of the girls. She much prefers the company of men.