I just happened to be watching an episode of Bewitched (entitled "Divided He Falls"), when to my surprise I noticed a line of dialogue that Darren says is "Fun, Fun, Fun". Check it out at 14:02:
https://youtu.be/g3CvHA98kJAWas Fun x3 an actual term/expression before The BBs' song? I suppose it could just be a coincidence, but I feel like perhaps the terminology had weaved its way into pop culture - and thus this script - a mere two years later due to the song.
What does everyone else think?
Also at about 17:45 in the same episode, you can hear generic but vaguely BB- sounding background music at a party, just as Darren repeats the Fun x3 expression twice more in a row... and at 18:10, Samantha dismissively mutters Fun x3 yet once more