Frank's side made a disastrous start as Kenny Tete put Fulham ahead before Harry Wilson's superb strike punished a calamitous blunder from Vicario.
Vicario was barraged with jeers from furious Tottenham fans as soon as he touched the ball in the immediate aftermath of the goal.
Tottenham were booed off at half-time and although Mohammed Kudus got one back after the interval, there were more taunts at the final whistle.
"When you're in a bad spell, everything seems to go against you. The second goal is a mistake from Vic. I didn't like that our fans booed at him straight after and a few times after that," Frank said.
"They can't be true Tottenham fans because everyone supports each other when you're on the pitch and we do everything we can to perform.
"It is OK that they are frustrated, because we haven't won at home for a long time. We all badly want to win so I'm fine with them booing after the game, but during the game I hope it was one incident and it never happens again. That is unacceptable in my opinion."
Tottenham defender Pedro Porro appeared to make an angry gesture towards the supporters while walking off the pitch and Frank added: "I didn't see the incident so I don't know exactly.
"We are in a tough spell right now and for my players it is about being as calm as possible and doing everything we can to work through it."
With only three wins in their last 13 games in all competitions, Tottenham have slumped to 10th place in the Premier League.
Frank insisted this week that he was confident Tottenham's home form would eventually "click", but they have just three league victories in north London in 2025.
Tottenham are without a Premier League home victory since the opening weekend of the season, wining only four of their 10 matches in front of their fans in all competitions this season.
Tottenham's 4-1 loss at archrivals Arsenal last weekend and a 5-3 defeat away to Paris Saint-Germain in the Champions League on Wednesday had added to the pressure on Frank to end their home woes.