Sometimes, but sometimes I have been fooled by people I thought didn't toke, but did, and vise-versa too. I hate the tricky ones who you think toke, then when you ask them to join you for a joint, they're like, "That shit makes you stoopid, heh heh"

If someone is stoned, I can usually tell. Red eyes, dry pasty mouth, and a grin on their face, but I can't usually tell if a person smokes weed, just when they're high.