The word bidon has a lot of meaning. The first one is not colloquial: un bidon is a canister, a can, a jug. It also is a colloquial, slightly childish word for “belly”, just like bide.
But the meaning I want to talk about is very common slang: as an adjective, it means “fake”, “phoney” or “rigged”. Note that it is usually invariable: it stays bidon even in the feminine.
Les sondages, c’est bidon, j’y crois pas.
Opinion polls are sham, I don’t believe in them.
Les politiciens font plein de promesses bidon.
Politicians make a lot of bogus promises.
The verb bidonner means “to rig”.
Je suis sûr qu’ils ont bidonné les preuves.
I’m sure they faked the evidence.
For some reason, se bidonner has a different meaning: “to laugh”, which sounds a little childish to me, just like rigoler. Bidonnant therefore means “funny”.
On s’est bien bidonnés en regardant le film.
We had a lot of fun watching the movie.
Listen to the examples: