I think it is a reverse harem, romance, school life manga or something like that and most likely ongoing (hasn't been updated in long time). Its about this girl that is used as a lacky and there are these 3 boys that are seen as delinquents in the school, and on the 1st chapter the girl accidently trips and pulls the one guys pants down and after that they became friends. I also think the guys may have had the same last name, like satou or something. As for what the guys look like, one was a year younger and wore a labcoat and glasses, the other had blond hair and ear piercings, and the last one was tall, had scary looking eyes, and usually wore a jersey.
If you think you know this manga thank you ^^

It doesn't fit your description exactly, but you might be thinking of Ah! Itoshi no Banchousama. I'm not certain, so I'll try looking for one that has the details you're mentioning.