Last Cyborg: "What was Fun It all about then?"
This is only a guess here - F-U-N?
It was an update/adaptation of that old kindergarten song:
If by chance you meet a frown,
Turn that frown upside down...
Don't shun it,
Fun it...
I have never heard that nursery rhyme ever.
But, he was trying to ask, why was Roger annoyed at the "funk" of AOBTD if he wrote a funkish song (and of less quality than AOBTD) already?
Roger was only miffed at Another One Bites The Dust, because of all the royalties he missed out on. He didn't speak to John Deacon for years, using Brian as a go-between.
It wasn't until Roger's A Kind Of Magic became a big seller that the rift started to heal. By which time, John had wangled it so that the royalties were split four ways. This would normally have started off another period of silence between the two, but they used their new found maturity to settle their differences with a 'falls count anywhere' wrestling match. Roger won this matchup, pinning John after catching him unawares loading his car in the Surrey Quays Tesco car park.
As for 'Fun It', Roger wrote this with a sinister motive. Play it backwards and place a bucket over your head and you can clearly make out the words: "Die, Gary Jacobs, die".
Gary Jacobs was an infamous figure at the time, well known for instigating the Shadwell Riots - a campaign demanding the introduction of the leadless pencil - which caused one police officer to suffer a blistered finger, and startled a passing pigeon.