Green’s Dictionary of Slang

doormat n.

[the heavy beards that veterans of the Crimean War (1854–6) wore against the Russian cold. These were cropped short when the soldiers returned to the UK]

1. a short cropped beard.

[UK]Hotten Dict. of Modern Sl. etc. xlix: The ‘fast’ men of buried Nineveh, with their knotty and door-matty looking beards, may have cracked Slang jokes on the steps of Sennacherib’s palace.
[UK] in Punch 8 Oct. 165: My general name among chance acquaintances is ‘Old Doormat.’ You can judge how thick my hair must be.
[UK] (ref. to 1850s–80s) J. Ware Passing Eng. of the Victorian Era 115/2: Door-mat (Colloquial, 1856). The name given by the people to the heavy and unaccustomed beards which the Crimean heroes brought home from Russia in 1855–56, and which started the beard movement [...] By 1882 the term came to be applied to the moustache only, probably because about this time the tendency to shave the beard and wear only a very heavy moustache became prevalent.
[Aus]Bulletin (Sydney) 17 Oct. 5/2: The blithest stroller on the Block / Will have great doormats on his chin.
[UK]Hull Dly Mail 25 June 11/1: The Juge d’Instruction ran his fingers through his doormat of a beard.

2. (Aus.) a woman's short hairstyle.

[Aus]Bulletin (Sydney) 23 Apr. 8/4: The girl with the ‘door-mat’ hair and cardinal ‘oh-we-never-mention-’ems’.

3. a moustache.

see sense 1.

SE in slang uses

In compounds

doormat (thief) (n.) (also doormat grafter, doormatter)

a petty or incompetent thief.

[US]J. Flynt World of Graft 47: Nine out o’ ev’ry ten pinches is East Side doormat thieves.
[US]H. Hapgood Types from City Streets 318: Now I’m little better than a door-mat grafter.
[US]Hostetter & Beesley It’s a Racket! 223: doormat—The cheapest form of sneak thief.
[US]W. Smith Bessie Cotter 230: Not Cardy. Not that doormat grafter.
[US]Goldin et al. DAUL 60/2: Door-matter. A very petty thief, as one who would steal a door mat.
C. Lederer Never Steal Anything Small [film script] I ain’t doin’ this for you, you doormat thief [HDAS].