The African nation were being battered in a must-win match against the Balkan side and were four goals and a man down with a minute left on the clock when the QPR left-back, 30, snapped.
He whipped in an inch-perfect cross for substitute striker Pierre Webo to crash against the crossbar via the ground and his overhead kick follow-up could not be directed past his Croatian marker.
After the attack has dissipated, Assou-Ekotto went over to Ben Moukandjo - who had been lingering on the edge of the box when the defender had crossed for Webo - and started shouting at him.
Moukandjo attempted to walk past, looking downtrodden, but Assou-Ekotto suddenly lent in to attack the 25-year-old, who looked shocked at the more experienced player's antics.
The referee and his fellow officials missed the incident, so Assou-Ekotto has so far escaped being reprimanded, while injured Cameroon skipper Samuel Eto'o could be seen comforting a distressed Moukandjo after the final whistle.
Earlier in the first half, Alex Song had shown similar aggression when he had elbowed Croatia striker Mario Mandzukic in the back for no real reason, resulting in the Barcelona midfielder being given a straight red card with most of the match to play.
Cameroon boss Volker Finke was baffled as to why Song and Assou-Ekotto lashed out violently and said sorry for the way that his side crumbled - both on the scoresheet and psychologically.
"It's unimaginable," the German told reporters. "I saw this happen and I need to find out exactly what happened, why exactly these two players exploded.
"I hate to see that. It's not the image of Cameroon I want to project.
"I apologise for the result, it really hurts. We had no control on the game and I didn't like the behaviour of my team. We have to look forward - this team does have players for the future."The defeat in Manaus saw Cameroon become the third team to be eliminated from the World Cup, despite them still having a game against Brazil to play on Monday.
Their tournament has been plagued by an internal dispute over potential win bonuses, which ultimately proved pointless as the Indomitable Lions look set to exit the competition without a victory.