It is revealed during one of the Ranger Quests that he has been afraid of Pokémon ever since he was scratched by a Slakoth as a small child. This fear has developed into a belief that all Pokémon want to attack him. During said Quest, his wife asks the player to bring a Slakoth to him so that his fear would go away. Later, he tells the player that he's now able to pat Bidoof on their heads.
Calm Down Miltank
Vientown Little Tim
I got asked to do the milking. I surely would, even though I'm deathly a-scared of Pokémon, but our Miltank's gone all feisty on me... Can you go to my farm and calm down my Miltank?