Saitama meets a group of villains in a public restroom who mistake him for their ally, they introduce themselves to Saitama, but when he reveals he's a hero, attempt to defeat him.
Where to Watch One Punch Man: OVA 2 #01 Saitama to Sokosoko no Noryokumono-tachi
Cast of One Punch Man: OVA 2 #01 Saitama to Sokosoko no Noryokumono-tachi