While taking Amtrak from LA to Portland one summer years ago, this guy started chatting with me in the viewing car. We talked for a bit, we went to the bar and bought a few drinks together. Came up to a 20 minute stop at a station, and we got off together for a smoke.
That's when I saw the platform was full of cops ... who immediately began walking towards us.
And they grabbed him. Took him away. Turned out that before he ran into me, he'd spent the entire train ride trying to lure kids into the bathroom with promises of candy.
TL;DR: Spent a few hours on a train being friendly with a child molester.