The reason this happens is because Toby had forced Temmie to create concept art of him after one of his other friends told Toby that they wanted a muscular character. And knowing that temmie hated drawing horses and muscles, the answer was pretty clear
*Frisk doesn't have abs. Or the player is playing undertale as undyne or asgore? They are the only 2 undertale characters i know who has sculpted abs, above aaron*
When I was a beginner, I used to praise Timmy, and now that I'm a professional, I just tell him, "Howie!!!" Oh and since you've raised your Lv get ready to have a bad time I'm just kidding I hope you have a nice day