Suarez brought shame on Liverpool last weekend when he refused to shake Patrice Evra's hand ahead of the Premier League defeat at Manchester United.
The South American was eventually forced into an apology after Reds managing director Ian Ayre said Suarez had misled the club about his intentions.
It is the latest in a long line of disciplinary woes for Suarez, who only last season was banned for seven matches by the Dutch FA for biting PSV Eindhoven's Otman Bakkal while playing for Ajax.
De Boer was assistant to Martin Jol at the time of the incident, in November 2010, but has since assumed full control at Ajax and sanctioned Suarez's £22.7million departure for Liverpool in January last year.
"Luis is a winner," said De Boer. "Outside the pitch he's a fantastic player and person.
"In the game he does everything to win but sometimes he does some stupid things.
"I don't really know the details of what happened in that (Saturday's) game so I can't comment.
"But I don't think it was very smart that he didn't shake Evra's hand because it puts more attention on everything."
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