What I would do:
Conan- Run up to him, hug him, and if he's alone, scream 'Shin-chan', watch him squirm, and then tease him about Ran.
DB- Kick aside Ayumi and Genta and hug Mitsuhiko. Same treatment as Conan.
Ran- Be friends with her cuz she reminds me of my best friend (course, my best friend has no bf). I'd tease her about Shin-chan.
Ai- Make friends with her too cuz she reminds me of me. Held-back, cold, reserved, guy we like who we know might (or in her case definitely) like someone else even though we're really close to them.
Kogoro- Ignore.
Heiji- See above at Conan, plus some comments hinting at HeiShin and Kazuha. Let's see which one makes him blush more.
Gin- Takes gun and shoots.
Vermouth- OMG you're so awesome! You're my fav BO character! *watches her get all confused. Ducks bullet*
Kaito- Hey Kaitou Kid! Watch him squirm.
Basically, I would be weird and torture them.