From the Super Mario Wiki
“It's a Sonny day!”
Sonny is a peppy human male golfer in the Mario Golf series. His only appearance being in Mario Golf for the Nintendo 64, he is the third character unlocked in the Get Character mode. Sonny's attire consists of a red polo shirt and tan pants, as well as a brown cowboy hat. The only times he is seen without his hat is when the player scores an eagle shot or higher, to which Sonny will toss it off and exuberantly shout "Yahoo!", or, if having scored a bogey or lower, will hang it in shame with a resenting "Oh, no!".