Only once!
In the 70's I was persuaded by my then flatmate who was an Aberdeen supporter to go with him to Parkhead to watch them play celtc (Aberdeen end obviously).
Somehow Aberdeen won and we headed back to our local, Neesons on Alison Street where he was the token Dons supporter and I was the token bluenose.
We obviously kept the celebrations low key but later on in the evening somehow Simply The Best got played and after 7 or 8 pints of The Protestant Porter I concluded the song with a very loud FTP!
Not my most sensible decision as I got 50 shades of shite kicked out of me!
My conclusion?.....going to watch celtc is hazardous to a chaps mental and physical wellbeing!