WHEN an invitation arrives to party with Fred, Wilma, Barney, Betty et al, you expect - by the very homespun nature of the names - that it would be a rather sedate affair. Not so, it seems. For (in case you're not clued up) these are the Flintstones, the zany and zippy TV characters, which means it's going to be pretty boisterous over at the China Jump tonight. Club owner John Green told us the Flintstones were his favourites on the telly both as man and boy - which is a pretty grown-up confession to make. So we can excuse him his indulgence. Green would like the rest of us to join in the fun tonight by turning up dressed as one of the Flintstones. Which means one or two people we know can proceed to the China Jump straight from their office. Green said: ''There'll be lots of prizes for the daring, including a trip to Malaysia.'' Yabadabadoo . . .