One Piece Chapter 6, page 15: Chapter 6: Number One

While still mid-air, Luffy delivers a powerful flying kick straight into Captain Morgan's face with a solid "WMP.." and "UNGH!" impact. The force of the blow sends the massive Marine captain sliding backward across the dirt yard, leaving a trail of dust with a loud "SKKK!!" sound effect. The watching Marines are left speechless, stammering, "TH-THE CAPTAIN..."