Green’s Dictionary of Slang

lawn n.2

1. a crew cut hairstyle; thus lawnhead, a person with a crewcut.

[US](con. 1945) E. Thompson Tattoo (1977) 424: In about ten minutes the lawnhead came back [...] A blond crew cut like a brush had been mowed level as a putting green.

2. (gay) pubic hair, and if it is shaved it is a mowed lawn.

[US]Trimble 5000 Adult Sex Words and Phrases.
[US]Maledicta VI:1+2 (Summer/Winter) 131: Pubes […] grass, lawn, mowed lawn if shaved.

In compounds

lawn-mower (n.)

(US) a cunnilinctor.

[US]B. Rodgers Queens’ Vernacular 139: lawnmower the mouth of a cuntsucker.
[US]Maledicta VI:1+2 (Summer/Winter) 134: sneeze in the cabbage (modern give head as a lawnmower or bumper sticker, etc.).

In phrases

mow the lawn (v.)

1. (US black) to comb one’s hair.

[US]D. Burley N.Y. Amsterdam News 18 Sept. 22: When you’ve mowed your lawn righteously with that Jesse James Killer, lay your mellow roof into the sack.

2. (US) to shave with an electric razor; thus lawnmower n.

[US]P. Kendall Dict. Service Sl. n.p.: lawnmower . . . a razor.

3. to perform cunnilingus.

closesupport posting 10 Sept. Cyclingforums.com 🌐 Mowing the lawn [...] its a killer when your trying to ride and you’ve been trying to hawk up a pubic hair most the day.

4. (Aus./UK) of a woman, to shave or trim the pubic hair.

[Aus]N. Keesing Lily on the Dustbin 40: Few girls desire ‘a forest’ or ‘mohair stockings’ and will assiduously ‘mow the lawn’ to control them.
UrbanDictionary.com 7 Aug. 🌐 mowing the lawn When one shaves off all of his or her pubic hairs.