Truck-kun, also known as Truck-sama and Truck-chan, is a nickname given to trucks involved in fatal accidents in various anime and manga stories. The name was coined online after users on the /r/manga subreddit pointed out that truck accidents were repeatedly used as plot devices, most notably in the manga Fuuka.
On April 14th, 2015, Redditor poloport submitted a thread titled "Trucks in Manga," featuring a page from the manga Re: Marina in which a truck is shown speeding toward a person crossing the street (shown below). In the comments of the /r/manga post, Redditor shwag945 replied "Oh truck-kun you are my favorite plot device."
On May 19th, Redditor Draaly-Throwaway submitted a post to /r/manga asking which character from a story they would "introduce Truck-kun to." On February 1st, 2016, an anonymous 4chan user submitted a thread titled "Japanese Truck," which encouraged others to post manga pages in which characters are hit by a speeding truck (shown below).
On February 7th, 2016, Redditor Xx255q submitted a post asking "How many deaths has Truck-kun Cost?" to /r/manga. On January 6th, 2017, TV Tropes Forums user TendouMan submitted a thread titled "Truck-kun: The most prolific serial killer in Japanese popculture." On February 19th, Redditor 316KO submitted an entry asking "What's Truck-kun?" to /r/manga, to which Redditor Tehbeefer cited the "Look Both Ways" page on TV Tropes.