I did this with my friends when we went to Thailand. We were enjoying the delicious taste on a beach, two Australian guys were wanted to try it. They both spat it out instantly and the other one got so mad we thought he’s actually going to attack us.
After he calmed down a bit he demanded to see us drink it to be sure we hadn’t tricked him to drink poison. So we downed the entire 1 litre bottle to appease him. It was the start of a great day that lasted for few days.
He was married and had kids. He never showed any violent tendencies and was physically very non-imposing. I always assumed that manipulation and mental games were his primary tools, but one can never really know.
His eyes seemed pretty normal, but I remember that they were always moving. He wouldn’t look you straight into eyes for more than a second or two.