You are an extroverted, easygoing, flighty, life-of-the-party teenager dude who can easily charm the pants off of ladies of all ages. You've probably been dating girls since you started walking. You have a bro, he's a wallflower. Shy flower boy, never in the spotlight, a sweetheart, never fell in love though.
Then you noticed for the first time that your bro found a girl he likes. She's kinda interesting, different, seems to treat him well enough. They've a got a good vibe going. By the way, by "bro" he's not just a bro he's literally your twin brother. Now what do you use your maxed out CHA stat for?
A) Be the wingman of the century. Wins Nobel Peace Prize.
B) Write a blog about their budding romance. Your cellphone novel becomes extremely popular and you start a career as successful novelist.
C) Chill out and tease him from time to time. You got your own life to live, man.
D) Try to compete with him for the girl's attention, use your superior experience to preempt his clumsy attempts at taking initiative, and imply you like the girl to coerce him to back down. It makes sense you know, the girl is probably the first to treat your bro like a human after all. She's different from the girls you dated, she's got great character! Shut it Brendan Rodgers!
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Now I'm not saying you can take "dibs" on people -- people ain't property, feelings are free, all's fair in love and war, etc., etc. -- but come on. Dude. What the fuck.