Green’s Dictionary of Slang

1. a fool, a simpleton [= mug n.¹ (2a)].

1998

R. Puxley Fresh Rabbit.

2. a drinking mug.

1972

Dodson & Saczek Dict. of Cockney Rhy. Sl.

3. a bedbug.

1976		(ref. to 1930s) R. Barnes Coronation Cups and Jam Jars 57: They were also known as Hearth Rugs, or Steam Tugs to the well-initiated.
1998		R. Puxley Fresh Rabbit.