Green’s Dictionary of Slang

loaf v.2

[loaf (of bread) n.]

(Irish) to headbutt.

[Ire]F. Mac Anna Last of the High Kings 93: Vinnie loafed Frankie on the nose and Frankie staggered back.
[Ire]R. Doyle Van (1998) 587: Jimmy Sr’s heart was loafing his breast plate.
[Ire]F. Mac Anna Cartoon City 2: The first and most important lesson a tall guy learned was to steer clear of fights with guys small enough to loaf you in the balls.