Fred is the most unlikable and mean-spirited member of the team. It doesn't help that he is portrayed as like a jerk jock.
Fred can be creepy towards Daphne and Velma. While inside Daphne's body, he says, "Hey! I can look at myself naked!", which disgusted Velma. He also tells Velma, "I'm a man of substance. Dorky chicks like you turn me on, too.".
Fred doesn't seem like a good leader. Him disagreeing with Velma, Daphne, and Shaggy resulted in Mystery Inc. disbanding for two years.
While Fred was trying to expose Heather Jasper Howe for taking things out of context, he inadvertently said "I think Coolsville sucks!" where the news portrayed him as a villain.
Fred berated Scrappy-Doo for marking his territory on Daphne, causing him and his team to get rid of Scrappy-Doo by a desert all alone.
In the second film (Scooby-Doo 2: Mystery Incorporated), his hair is nowhere as blonde as in the first film or the animated series.
Despite a good performance, Freddie Prinze Jr. was miscast.
In the first film (Scooby-Doo), he looks very similar to his animated counterpart complete with blonde hair and an orange ascot.