Kylie Travis is fleeing from a gun-toting serial killer (James Belushi with a truly rotten Texas accent) when she stumbles into a time machine that zaps her back 20 minutes, to listen to Belushi's dreadful blow-job jokes all over again.
Retroactive is one of those movies that you think is going to be pretty terrible, but then it turns out to be much, much worse than you could have expected. The time machine doesn't send you physically back in time, it just zaps your mind back in time, so you remember stuff that hasn't happened yet. The big trope is that every time Travis goes back and tries to stop Belushi from killing a lot of people with his godawful attempt at a Texas drawl, she just makes things worse and he kills more people as a result. And every single time, she has to listen to Belushi explain how his belt buckle would look better pressed against a woman's forehead. Yee-haw!
Of course, Belushi's psychotic Texan finds his way into the time machine, and goes back a few times as well, but he doesn't take advantage of his knowledge of the future to become actually interesting or anything. Instead, he just chews more and more scenery. It all culminates in this fantastic scene where Belushi explains what he'll do with the time machine once he masters its operation:
Ah, James Belushi. What would we ever do without you?