The Fighter for Hire - Sanosuke Sagara (S01E04)

enshin, Kaoru, and Yahiko visit Akabeko, a beef hot-pot restaurant, where a group of democratic rights activists gets into a heated argument. One of them throws a bottle of sake, and it hits Kenshin, causing a commotion. Sanosuke Sagara, who happened to be in the store during the quarrel, stood up and blew away the activists with a single flick to the forehead. Seeing Kenshin's strength, Sanosuke's curiosity is roused and he asks, "You wanna buy a fight from me?" (Crunchyroll)