Stupidity: Someone with the Punisher's tactical knowledge would not hang upside down from a chandelier to shoot in a 360-degree pattern at his targets. This would make him a sitting duck and it's only because of the movie tropes of Stormtrooper aim and cannon fodder henchmen that he isn't killed because of it.
Stupidity: Near the end, Sydney Wells and Paul Faulkner try to rescue a little 10-year-old girl who is trapped in the recreational vehicle. Sydney is banging on the door from the outside while the little girl is banging on the door from the inside. Paul then smashes out the door window, reaches inside and easily releases the door latch in one move. So, a 10-year-old girl was "trapped" because she couldn't simply open a door latch? Stupid.
Stupidity: At the end of the film, Abel had nothing to gain from lying about having a gun to the police officer. He had no way to prevent Chris and Lisa from presenting the informant's cell phone and exposing his involvement in the break-in and vandalism of the couple's house. Additionally, testing from the shots fired in the house and the car would prove that there were two different guns involved. As a long time police officer, Abel should have known that giving up the gun would have been the easier way out instead of lying about it.
Stupidity: When she leaves him at home with a sandwich she says people will come check on him. When she gets home and he's not there, she doesn't go and ask those people where he is.