My favourite one is that water rotates in a certain direction when it goes down the drain. This direction is dependant on which hemisphere you live. This is complete garbage which most people can debunk. Do it for two sinks and half of them will go different ways! If they go the same way it is not hard to get them to go down the other way. Just rotate the water slightly before pulling the plug.
It requires a hugely careful set-up to actually detect Coriolis forces in this way, but it can be done. You need a large diameter vessel, with an outlet in the centre - the larger the diameter the better. It needs to be as far as practical from the equator; and it needs to be sheltered from external forces such as breezes and drafts, and allowed to settle for at least a day after filling, in a temperature controlled environment. We did this with a 2 metre diameter vessel in Leeds (which is about 54
o North of the equator); after three days of settling, and with the addition of a few drops of dye to make the movement more easily visible, the outlet was carefully opened, and the rotation was indeed in the anti-clockwise direction expected, in all three repeats of the experiment. It takes a long time for the rotation to be apparent at all; after about a third of the water has drained away, the conservation of angular momentum amplifies the effect enough for it to be noticeable.
I very much doubt that you could detect the effect in an ordinary sink, bathtub or WC, even using a statistical analysis of thousands of trials looking for a small bias in the expected direction.
