While Goku is known for being perhaps the strongest mortal in the universe, he does have one weakness that caused him to be defeated by Dragon Ball’s weakest fighter (and it’s pretty embarrassing).
Upon Goku’s introduction in Dragon Ball chapter 1, he was immediately presented as someone who couldn’t be defeated. Goku soundly beat every challenger he came across while Goku traveled around the world with Bulma in search for the Dragon Balls. Whether it be a shape-shifting villain, a low-level gang, or a fascist organization, Goku defeated them all like it was nothing. While he would face increasingly tougher challengers as the series progressed–especially in the Dragon Ball Z and Super eras–Goku more often than not always managed to break through his personal barriers and come out on top. However, in one episode of Dragon Ball GT, that trend came to a crashing halt in the most humiliating way imaginable.
Goku’s Secret Weakness is that He’s Ticklish
In Dragon Ball GT episode 41 (written by Atsushi Maekawa, directed by Osamu Kasai, produced by Toei Animation), all the Z-Fighters have decided to enter into the World Martial Arts Tournament–which is a pretty fun and significant callback to the days of classic Dragon Ball while also maintaining the importance of tournaments in Dragon Ball canon. Unfortunately, the ‘title fight’ of Goku vs Vegeta can’t happen this year as Goku was transformed into a child at the start of the series. This meant that Goku was stuck fighting literal children, which also meant that he would be able to claim the championship title in his division with minimal effort (not that Goku really cares about that). However, when Vegeta approaches Goku during Goku’s fight with a scared kid–as Vegeta wanted to break the rules and fight Goku anyway–Goku turned his back on his challenger and the kid pushed Goku out of the arena. Goku then held on to the edge of the ring to avoid being eliminated, but the kid proceeded to tickle the Saiyan warrior until he let go, and suffered a ring-out elimination.
While Goku didn’t really care about being the champion of the World Martial Arts Tournament’s kid’s division, he did care enough to hang on to the edge of the arena by his fingertips to not be eliminated. This means that Goku did care about participating in the fight at least to some degree, which also means that he didn’t just give up when the kid took him off guard. Essentially, Goku losing the fight because he was tickled was totally genuine, and he wasn’t just putting on an act for the sake of the clearly outmatched child he was challenging. This calls into question every fight Goku has ever been in. Could Frieza have prevented facing the wrath of a Super Saiyan if he had just tickled Goku rather than killing Krillin? Should Jiren have dedicated the last of his efforts during the Tournament of Power to locating Goku’s most ticklish spots? If Goku can’t even withstand being tickled by some kid, there’s no way he could fight off the immense tickling-potential of Frieza or Jiren.
Comical hypotheticals aside, the fact that Goku was forced to let go of the ring when he legitimately tried to hang on and stay in the fight because he was tickled proves that being tickled is one of his actual weaknesses–one which allowed Dragon Ball’s weakest fighter (that being some random, powerless kid) to beat him.