As long as your sister is an adult it's really not your business. The only thing you can and/or should do is tell her how you feel about him.
Calmy and warmly warn her that these sorts of things happen and let her know that your worried about her (because you care etc.) and a bit sus about the guy. There isn't much you can do unfortunately, she may end up being a more mature person because of it.
I was lucky and my sisters have so far been in normal long term relationships.
It's not that they can't.
It's that they have goals and your wallet stays a lot thicker when you don't have a woman in your life. When you're young, you want a sports car or a nice truck. You want to move into a real house out of an apartment.
entertaining women will make all of these goals harder and take longer to achieve because they are expected to pay for everything, leaving fuck all in their bank account. takes a while to work your way up to a job where you are swimming in $$
I remember when I moved out of my mother's. It was hard, working for what I wanted. What my parents had to work for, they could buy in a summer. What I wanted to work for, I'd have to work harder than they ever did all year for 2 years. After taking girls out on dates , buying them things and going out all the time with friends, I'd realize that I wasn't keeping as much money as I wanted.
I'd write this stuff down and be like "fuck. i just got the biggest paycheck of my career and i can't even realistically spend as much money as i want to if i want to buy that car next year"
"having a good time" to women is practically synonymous with "spending a dudes money". whether it's recreational drug use, hitting up a bar, driving out into the middle of fucking nowhere or just getting take-out.
Most women are never going to find a dude worth the time of day in his early years because the only ones standing out are impulsive morons burning up all of their money, overshadowing the guy who doesn't have time or his parents' money to be a fuckboy, busting his ass working for everything he has. Shit, he probably doesn't have enough time in the day to give a woman the attention that she wants because she is so high maintenance and needy.
Maybe if you don't care about them at all, sure.
But most sane family and friends get upset seeing their friends and family upset, so yeah, it is kinda in a way "their business", more like it's kinda expected of good friends/family to give warnings, even if they're not always accurate.
Maybe he's met the guy a few times and seen how he acts?
"El Psy Kongroo!" Hearthstone Moderator
shes a moped.
She's an adult. Tell her how you feel and then leave it alone.
I doubt there is anything you can do. Telling her about him and warning her would just drive a wedge between you two. Even if it turns out you are right, she may still be angry at you.
Just let it go. If he ends up banging her once and leaving, talk to her and try to use this as a lesson. But this only works if your sis can learn from mistakes.
You can also go teh big bro route and pull dude to the side and give him "Tha Speech". I always wanted to do that myself.
Okay? But your question was how Bigzo would know, and does his sister talk to him about her sex life.
I was pointing out there's other ways to tell, like if when she first introduced him, he wasn't acting right. First impressions are huge, and if someone seriously cares about the person they're dating, they should be aiming to make a good first impression.
Maybe the guy came around acting like a jerk.
"El Psy Kongroo!" Hearthstone Moderator
How much you wanna bet that if you ask her why is she with the guy, she'll say, "Hey it's my life. Mind your own fucking beeswax!" or some such?