Spurs' domestic struggles mean the Australian has presided over the club's worst ever Premier League campaign with a record tally of 21 defeats, but he also stands on the brink of the holy grail - eagerly-awaited silverware.
The embattled head coach conducted a fiery press conference at San Mames ahead of the showdown with Manchester United.
Asked about the fine line between "infamy" and "legendary status", Postecoglou, referencing a newspaper article which said he was "teetering between hero and clown" depending on the outcome against United, snapped: "I'll tell you one thing, irrespective of what happens tomorrow, I'm not a clown and I never will be.
"I'm really disappointed that you would use such terminology about a person who for 26 years without any favours from anyone has worked his way to a position where he's leading out a club in a European major competition (final)."
With Tottenham down in 17th in the Premier League, Postecoglou admitted last month the "general sentiment" was he would leave, even if he ended the club's 17-year trophy drought, but he felt his work in north London was far from finished.
"I don't think my job is done here," Postecoglou said.
"I really feel like we are building something and what a trophy does is hopefully accelerate that. So I still think there is work to be done.
"It is quite obvious with the challenges we've had this year, which I think are well chronicled,. There is some reasoning in the context of that, but also there has been some growth I would like to see through.
"Whether that happens or not is not that important right now, but far from it is this job finished. I certainly feel there is some growth there that we can take this club to where it needs to be.
"I've been in this position before where the big game was the last game I managed. It's not unusual territory for me.
"I have always navigated it pretty well because, for me, nothing is more important than my responsibility for this football club and its fans that tomorrow me, the players, our mind is only on one thing and that is to create something special."
Postecoglou played down Lucas Bergvall's chances of being fit to face United after an ankle injury, with James Maddison and Dejan Kulusevski (both knee) also sidelined, but Pape Sarr is available.
The big choice for the Australian ahead of his 100th game in charge of Spurs is who will provide creativity in a three-man midfield alongside Yves Bissouma and Rodrigo Bentancur.
Wilson Odobert was used in the attacking midfield role at Aston Villa, but another alternative is to drop Dominic Solanke slightly deeper.
Despite continuous discourse over his future, Postecoglou will not lose focus on Tottenham's chance to taste European success for the first time since their 1984 UEFA Cup victory.
"Whatever happens beyond tomorrow is kind of irrelevant when you think about the opportunity that exists right now," Postecoglou said.
"That opportunity is to provide something special for the football club, for the supporters and for everyone who has worked so hard.
"Not just this year, but for the 15, 16 years, however long it has been without a trophy and also the 41 years without a European trophy.
"I'm pretty good at just making sure all my focus is on giving this football club the best opportunity that it's had for a while to do something special."
Meanwhile Brennan Johnson played down Tottenham's past wins over United but is confident they will formulate a new plan to secure Europa League glory.
Spurs have defeated United three times this season and twice since Ruben Amorim took over from Erik ten Hag in November.
A 3-0 win for Tottenham at Old Trafford in September pushed Ten Hag towards the exit door before Amorim watched his new team go down 4-3 in the Carabao Cup quarter-finals in December, while the most recent battle in February finished 1-0 to the north London club.
But Johnson insisted: "I think we know, going into the final, we can't rely on the fact that we've beaten them a few times this season.
"I think it's about now coming up with a plan because each time we've beaten them has been down to different reasons.
"I feel like we've done good work preparing for Man United so now it's about coming up with how we want to win, things we want to do, things we want to stop them from doing so it's a new opportunity.
"We want to prepare and be as confident as we can. When times have been tough and we've had to go to some tough places in Europe and got some really good results, it brings the squad together a massive amount.
"The quarter-final, the semi-final, these games have been massive for us. Unbelievable victories, real togetherness and yeah, it just make us stronger and more together."