flex

To "flex" literally means to contract a muscle, but in contemporary slang, it means to show off or boast about one’s possessions, achievements, or status. The mental image is someone physically tensing their bicep to draw attention to their strength, metaphorically applied to flaunting wealth, expensive clothes, or social influence. While "flexing" can be used neutrally to describe someone simply highlighting their accomplishments, it often carries a slightly mocking or critical tone when used to describe someone who is being arrogant or insecure. It is frequently used in the phrase "weird flex, but okay" to acknowledge that someone is bragging about something bizarre or unimpressive.
In conversation
Discussing a new purchase
Check out my new watch, it cost me two months' salary.
Check out my new watch, it cost me two months' salary.
Okay, we get it, you're flexing.
Okay, we get it, you're flexing.
Used here to call out someone for showing off wealth.
Acknowledging a strange boast
I haven't slept in three days because I was playing video games.
I haven't slept in three days because I was playing video games.
Weird flex, but okay.
Weird flex, but okay.
A common retort when someone boasts about something negative or weird.
Examples
He is always flexing his expensive car on Instagram.
He is always flexing his expensive car on Instagram.
It is a major flex to get into that university without any extracurriculars.
It is a major flex to get into that university without any extracurriculars.
Don't be so insecure that you feel the need to flex your status to strangers.
Don't be so insecure that you feel the need to flex your status to strangers.