These were recalled to me from years past when my son who was working out in the oil field in Midland mentioned to me that those guys would bet on anything. A lot of time on their hands + a lot of money too. So I told him a few that I recalled.
1- Get the bartender to hold 2 pilsner glasses underwater in the sink, holding the 2 glasses lips together to make a seal. Take them out + gently put the bottom glass into an old-fashioned whiskey glass. Now, you bet the other guy that you can get all the water out of the top pilsner glass into the old-fashioned glass without spilling a drop on the bar. Of course, he bites, + when he does
you get a cocktail straw + gently start blowing around the rim + the water from the top glass slowly dribbles past the seal into the old-fashioned glass.
2- Lay a pool cue across the narrow sides of the table + roll a pool ball back + forth to show that there is no way that the ball can go under the cue unaided. Then you bet that you can do just that, roll the ball under the cue without touching the cue. They bite at this one too. Make a big show of moving the ball back + forth while keeping an eagle eye level with the table (draw it out), + finally back up + roll the ball under the pool table.
3- Here's 2 that will usually get most folks, especially those who pride themselves on their biblical knowledge. The 1st is to bet that they can't name how many animals of each species that Moses took onto the ark. 99 out of a 100 will say 2 + just bypass that you said Moses instead of Noah. Simple psychological trick, but it works. The other biblical one to get them to bet on is that they can't name who cut Samson's hair? Again, 99 out of 100 will say Delilah, but they would be wrong. Look it up. Delilah hired men to come in + cut his hair while he slept (most likely passed out if the truth be known) but she never did it herself. On all of those + most other bets, the devil's in the details.

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answered, John.