Is it true that Jesus was really rubbish at backgammon and he never even beat John the Baptist once?

yes it it is true jesus was really bad at it because he was a leprcharn

Nope.

In fact, their last game, Jesus bet John that whoever lost would live in the wilderness for 1 year.

When he found John about 9 months later, John was still pissed and pushed him in the river.

That's where the whole baptism story came from.

Says so in John 2, so I assume.

They used to baptize each other a lot. What was the fascination with repeated mutual baptism?

No that isn't true. Although their pinochle battles were epic from what I hear.

I have no evidence, therefore no opinion.