The Dockers had skipped to match-winning 40-point lead at the final break after kicking six goals in the third quarter against the dual reigning premiers.
"I was probably the most angry I'd been at three-quarter time in a long time, I just said what I thought, pretty much," Fagan said.
But after the game Fagan stressed the importance of keeping the loss in perspective.
"I don't believe that what we see makes a massive difference to motivation levels, I just wanted to dig at their pride a little bit,'' he said.
"We've just got to keep the context here. We've just played the team that's won 11 games in a row - they're going pretty good.''
The Dockers' quest for a maiden AFL premiership is continuing to gather steam after knocking over the Lions on their home turf, silencing a parochial crowd.
Fremantle extended a club-record winning streak to 11 matches, their 15.13 (103) to 10.18 (78) victory on Saturday leaving them a game clear on top of the ladder after 12 rounds.
Their only loss was to perennial contenders Geelong by 10 points in round one.
Fremantle coach Justin Longmuir said the Dockers went into the game knowing the Lions were vulnerable after heavy defeats to GWS and Geelong.
"I don't want to be disrespectful, because they've been in the last three grand finals, but they're not playing up to that level now, clearly,'' Longmuir said.
"So we felt there were some opportunities there, and we were able to take some of those."
The Dockers' win was even more impressive given it was achieved without midfield guns Caleb Serong and Hayden Young.
The only sour note was a knee injury to defender Brennan Cox, which was not thought to be serious, and a hamstring injury to Matthew Johnson, who did a superb tagging job on Lachie Neale.
The Lions' tilt at a second flag "three-peat" is well and truly on the skids, after yet another third-quarter fade-out.
Many of their best players - Neale, Hugh McCluggage and Josh Dunkley - were subdued.
They were blown away when the Dockers slammed on five goals in 10 minutes, crowned by a trademark goal on the run by "unicorn" ruckman Luke Jackson, following up his own centre-square work.
It gave the visitors a 40-point lead they would maintain at the final break, with the game as good as gone for the Lions.
The Lions pushed hard in the final term, kicking four goals to win the quarter, but Dockers forward Josh Treacy iced the result with his third major.
The Dockers were dominant in the air up forward, where Jye Amiss, Patrick Voss and Treacy bagged 11 goals between them.
Voss - a virtual decoy behind Treacy and Amiss - proved a massive handful with four, missing a couple of sitters along the way.
Amiss also kicked four, with Treacy pushing higher up the ground where his physicality terrorised the Lions.
At ground level, the Dockers were quicker, stronger and more aggressive, hunting the Lions into submission with a remarkably even team performance.
Stacked with elite talent in every part of the ground, their work rate made the reigning premiers look ordinary.
They were also ultra-disciplined in their set-up behind the ball, with only Darcy Wilmot able to pick his way through the purple maze regularly.
Once again the Lions looked lost without playmaker Dayne Zorko, sidelined for at least another month with a quad injury.
The loss of attacking half-back Keidean Coleman to a hamstring injury just before quarter-time added to the Lions' difficulties in defensive transition.
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