Depends on the context. There's a difference between using vulnerability as a life lesson vs using vulnerability to play victim.
There's levels to opening up. Certain things you should keep to yourself such as medical issues, personal/family problems, boundaries etc. People can use that as fuel against you.
It's true that men are supposed to be stoic, detached and calm as a rock. Not moved by reaction. Being temperamental vs being expressive is very different. Being temperamental is lack of emotional control. Being expressive is conveying thought or feeling, for example, musicians showcasing their talent, artists exhibiting their paintings, collages etc. There's nothing weak about expressing emotions it shows the person has a personality.
Just be careful who you open up too.