As soon as we got off the bikes a young Thai man on a motorbike came up from behind and stopped in front of us. I figured he thought one of us had a flat and he might may a few baht helping us get to a bike shop.
"Do you want cannabis?", he asked. I was surprised and thought I had misheard him, but he repeated it. "Do you want cannabis?"
"No, we just want to rest a minute and ride our bikes."
He was quite insistent and it took a couple minutes to convince him that we did _not_ want cannabis. He finally left and we went on with our ride. Sarge and I were a bit mystified as we hardly look like dope smokin' hippies.

At Borfai I turned back on to Phetkasem and as I was waiting to make the U turn I heard a motorbike beep several times. I looked over my shoulder and saw the 'salesman' with another Thai man on the back of his bike smiling and waving. I shrugged and rode home.
At home I called the missus and told her about it. Her immediate reply was that he was with the police. The entire situation was odd enough that her take on it is quite believable. I've been here about three and a half years and have spent more than a little time in both Farang and Thai bars and such, and have never been offered drugs.
The drug laws here are pretty harsh so please be wise and say 'no' if offered any kind of illegal drugs.