I don't remember what it was called, but I do remember that it was centred around a delinquent looking guy who sits behind a boy with curly hair and glasses. I think the delinquent has an obsession with glasses' neck.

Anyway, there's a whole motif about Delinquent cutting glasses' hair. The MC's best friend is good at cutting hair, is a side point. There's a train scene. Lots of kissing. That's about what I remember

I love this series, it's Endou-kun no Kansatsu Nikki and its continuation Endou-kun no Jikken Note. (Protip though, this thread belongs in the Yaoi/Yuri section)