Green’s Dictionary of Slang

1. to mess about, to play around.

1929

J.B. Priestley Good Companions 636: Yer doin’ right well, Leonard, an’ if you’d nobbut settle a bit an’ not go malachin’ abart so much wi’ t’girls —.

2. to deceive.

1954

J. Steinbeck Sweet Thursday (1955) 248: How do I know you ain’t malarkying me now just to make me feel good?