I don’t get the joke...
Well, it's just skinny wrongly, again, using the word bigot, when in fact he means racist...he's easily confused which, as a result, exposes his complete incompetence with the English language & he does so on a regular basis...too long spent with his mates at the mosque...
However, back in the 70's much of UK humour was racist-based, & a derogatory/ridiculing style which was prevalent in both everyday society, among working mens club comedians, professional entertainers/comedians, & even on UK TV (a series called Love Thy Neighbour was one such programme which springs to mind):
Whites would call Irish, thick, paddy, that sort of thing.
Blacks would call whites honky, snowflake, etc.
Whites would call blacks chalky, the now infamous 'N' word
People of Indian/Pakistani extract were also subjected to similar by everyone.
Of course nowadays we aren't allowed to use such humour. Luckily, it's had its day.