'Inappropriate behaviour' would have to be qualified. Go ahead.
It would be what the company deemed as inappropriate, they are not going to have bullet points for every single offence you could do are they Einstein, could you imagine the contract.
Inappropriate behaviour, this means any of the following:
Public order (which would need to be broken down)
Criminal damage (would need to be broken down)
Indecent exposure
Fighting
GBH
ABH
Domestic Violence
Violence against colleagues
Bullying
Robbing cars
Breaking into property
Slapping an elderly person
Kicking off wing mirror
You could go on for hours, they are not going to specially mention every thing you could do that would warrant a warning or be a sackable offence are they.
If you are just talking about social media, if they generalise it to no racism, no gender discrimination, no abusive or bullying intent and you then post a video of you doing something horrendous that is not in your contract, the company is screwed.
They will have it in the contract that it is at their discretion to decide on what they deem as inappropriate.
Do we now understand? Not rocket science to be fair is it.