Nice topic, Ghada... very fun to discuss! Well, Sirius was obviously great with the ladies and if he'd been in our school all the girls would surely have fallen for him! I tend to see young Sirius not really as someone who chases girls, but as someone who knows how to treat them (flowers, chocolates, the works, hehe!

) and who might have had multiple girls after him at any one time. Obviously, the good looks just say it all... *sighs* Well, basically I think he was really good with the opposite sex, but probably chased after them less than they chased after him! Though I doubt he would ever be without several prospective dates for every Hogsmeade visit/ball!
Sirius was probably quite serious (haha) because he knew from a young age that the world isn't full of good people (thanks to the pure-blood maniacs he lived with

) so he was mature from the inside and yet his good looks and popularity made him behave in a "haughty" manner, as JKR wrote in OotP. James probably made more jokes than Sirius, while Sirius' humour might have bordered on the more sinister or sarcastic style due to his inner hurt. While James had an ordinary childhood, Sirius' childhood was probably filled with a lot less love and a lot more loneliness and sadness, and their different upbringings shaped their characters. I have a feeling that most of the time, it was probably Sirius who went too far in his pranks, or caused James to go to far, as Sirius was definitely the more reckless of the pair.
Studies-wise, I guess Sirius was one of those couldn't-care-less-about-school type of dudes who might not have been in all the teachers' good books (lots of teachers - and students - don't really approve of students who fool around and still get great marks; I'm sure he got all Os without even trying - remember "I don't need to look at that rubbish, I know it all". Man... that line made me jealous. What I would give to not have to swot!) I'm sure he also went ahead of the class a lot since his brain was so quick that he wouldn't take long to get bored with what he was being taught and want to know more. So I'm sure he must have learnt how to conjure a Patronus at some point during his schooldays... maybe 6th or 7th year? Or maybe even 5th year... And I am positive it was a big black dog just like his Animagus form...
I agree that Sirius' favourite professor was probably McGonagall... though it could have been Flitwick or someone too, and I am sure that Sirius had high respect for Dumbledore. I bet Slughorn wished Sirius was in his house since he was so talented and came from a family of Slytherins. Slughorn definitely must have indulged him a lot because of his talents, and probably offered to give him a few choice Ministry contacts after he left school.
Wow... that was a long post!!
