9. Don - 28 Weeks Later
To be fair to Don (Robert Carlyle), he was at least under a lot of stress when he made this dumb decision in 28 Weeks Later, as he'd just fled his family while trying to escape a horde of rage-infected people. When he finally comes across his wife Alice in the hospital, he is overwhelmed with emotion, sneaking past a security cordon to speak to her and plea for clemency. He can't resist but give her a big kiss despite knowing full well what's been going on around him, and becomes immediately infected with the Rage virus. Y'see, Alice was an asymptomatic carrier of the virus, meaning that she could pass it on without being infected herself, and within moments, Don transforms, killing Alice along with a number of soldiers in the building. In the end, it was Don's love for his wife that was his undoing, clouding logic and reason just as it so often does.