Misinformation

You are not that far off. For me:

Hair grows everywhere except where you want it to.

It's a bit easier to gain muscles with the same amount of exercise and the same diet.

And yes, more irrational aggression to some degree.

Obviously not because of onions, though

I feel like there's this explot in human psychology:

1. People are pretty bad at matching causes to effects.
2. Doing something novel / outside your usual routine can feel pretty good, regardless of what it is you're doing.

Therefore: People who try weird diets, snake oils, or letting the sun shine on their asshole really do feel better afterwards, at least for a while. That must mean it works!