To compound his frustrations, the Liverpool fan was then kicked out of a pub as it was specifically dedicated to home supporters.
Roberto Firmino struck a hat-trick and Mohamed Salah scored for the eighth consecutive game - and what a goal it was, too - as Liverpool delivered a masterclass in a demolition on Claudio Ranieri's Premier League return.
Jurgen Klopp's side dominated from the outset to extend their unbeaten league run to 18 games, with Sadio Mane opening the scoring with his 100th Premier League goal.
Pimblett, 26, was at the game as a fan in the away stands and took to Instagram to voice his displeasure with the Hornets and their security teams.
He wrote: "Vicarage Road stewards on a power trip kicking us out for celebrating WOW!
"Cannot believe the audacity of these stewards singling us out when multiple ppl [sic] celebrated around us an escorted us out the stadium Watford do something about ur [sic] stewards."
He added: "Been kicked out of the match for celebrating and now we've been kicked out of the boozer by stewards because it is a home boozer.
"Watford, Ben Foster, I love you mate. But I hope Watford go down, youse are horrible, horrible."
'The Baddy' made a sensational debut appearance inside the Octagon last month against Luigi Vendramini as he knocked the Italian out inside a round.
'Suga' Sean O'Malley was mooted as a potential next opponent, but the Liverpudlian insists he wants to face a certified lightweight next.