Slaps Roof of Car is a popular phrasal template featuring a mock conversation between a car salesman and potential buyer in which the salesman emphasizes the phrase "this bad boy can fit so much X in it" by slapping the roof of the car. The phrase is frequently used as the caption to an illustration of a car salesman and the buyer.
On September 30th, 2014, Twitter  user @OBiiieeee tweeted, "Car Salesman: *slaps roof of car* this bad boy can fit so much f--king spaghetti in it." The post (shown below) received more than 7,700 retweets and 13,000 likes in four years.
Nearly a month later, on October 28th, 2014, Twitter user @Carlitos_N tweeted one of the earliest variations (shown below, left). They wrote, "Car Salesman: *slaps roof of car* this baby here can fit so much AHH! YO DID YOU SEE THAT SPIDER HANGING OFF THE MIRROR?! I'M OUT YO, I QUIT."
The following year, on February 26th, 2016, the website YourMechanic.com published an illustration of the stock photograph in the article "How to Effectively Deal With a Car Salesman" (shown below, right).
Three years later, on December 18th, 2017, Redditor  sweetums1313 posted the tweet in the /r/me_irl subreddit. Within seven months, the post received more than 13,300 points (91% upvoted) and 130 comments.
Several months later, on June 25th, Twitter user @MirGucci posted the original tweet as the caption to an illustration of a car salesman and a potential buyer. The post (shown below, center) received more than 875 retweets and 2,400 likes, reviving the meme.
Following the tweet, Redditors on the /r/dankmemes subreddit began posting variations of the meme. One of the earliest was posted less than 24 hours later, when Redditor Levardio posted a variation that criticized the subreddit, photoshopping the image to read "*slaps roof of format* this bad boy can fit so many f--king effortless memes in it." The post (shown below, right) received more than 13,000 points (96% upvoted) and 75 comments.