eveybody knows sirius has a reputation of being rebellious, reckless and just over all insufferable. if you have a bad idea, he'd be the first egging you on to get it done.
so imagine the schools' surprise when, the moment regulus starts out at hogwarts, suddenly they all get to see an elder brother in place of the dumbass teenager they know so well. sirius following regulus around whenever he gets into even the smallest tussle with his classmates or friends- "tell me who hurt u?!" "be careful, reg!" "dont hang with the wrong sort."
sirius seeking regulus out once a day to make sure he's okay, remembers to eat and to reminds him to sleep on time. sirius also goes out of his way to threaten regulus's friends to "take care of his baby brother or else."
regulus is sick and tired of his brother's hypocritical antics (he loves it- mostly), the skittles fear for their lives whenever regulus gets the slightest scratch- knowing exactly what (or rather who) is coming for him and sirius's friends just find this mother bird side of him very entertaining. (remus especially hmmmm i wonder why)
