It happened to me. Sitting at a light, foot on the brake slipped off and when I went to slam the brakes back on I stomped the gas pedal on my F-250. Ended up pushing a little old lady through the light and around the corner.
It does happen. Remember all of the “unintended acceleration” furor about Audis, back in the 80s? People were claiming that their Audis were running away with them, even when they were standing on the brakes as hard as they could. Investigations showed that the drivers were hitting the gas instead of the brake, then panicking and pressing the gas pedal even harder.