Okay, weird title, not fully explained in the video, but in this clip on the Johnny's couch/chair, after singing a song on the main stage, Maurice's guitar wasn't suitable for Barry to play their 1967 hit "Massachusetts". Why? Because Barry only plays guitar tuned to "Hawaiian tuning", hence them bringing out his own guitar (Barry doesn't read music, he plays by ear, and composes into a recorder, and has others (usually Maurice until he died) transcribe it).
Is that
Robert Blake who leans over on the left side of the screen near the beginning? Can anyone figure that one out, it looks like him.
In this clip, Maurice starts clowning around behind Barry & Robin, something he did perhaps out of an inferiority complex, because he never got to sing lead on any of the scores of Bee Gees hits, yet his harmonies and arrangements were critical to so many songs. The songs he sang lead on were unrecognizable as Bee Gees songs, and never released as singles, but there were usually 1 or 2 per album. A famous post I once made here years ago had everyone identifying a Maurice song as The Charlie Daniels Band. Some of you may remember that one

I had used an mp3 changer to change the coding of the artist, and title of the song (to "Southern Railroad", I think), and between the sound, style, and the mp3 coding, everyone was convinced it was Charlie Daniels, and then I had to go through a lot of hassle proving it wasn't.
YouTube - Bee Gees - Massachussets - Carson Show 73