Green’s Dictionary of Slang

(US) the hand.

1979		Maledicta III:2 159: German comb n A hand; from the alleged unsophistication of the Germans who used their fingers to straighten their hair.
1989		H. Rawson Dict. of Invective (1991) 171: Later generations produced such unflattering references as German comb, the fingers.

(US Und.) beer.

1909

F.H. Tillotson How I Became a Detective 88: ‘German delight’ means beer.

see separate entries.

(US) a beer belly, a noticeable paunch.

1935		A.J. Pollock Und. Speaks.
1943		‘Provincial Sayings’ AS XVIII:1 67/1: german goitre (a large stomach). S.C., N.C.
1950, 1965–70		in DARE.
1989		H. Rawson Dict. of Invective (1991) 171: Later generations produced such unflattering references as German comb, the fingers [...], German goiter, a beer belly.

vain boasting, megalomania, self-aggrandizement.

1909		J. Ware Passing Eng. of the Victorian Era 40/1: German gospel (Peoples’, November 1897). Bounce, vain boasting, megalomania. From a phrase addressed in this month by Prince Henry of Prussia to his brother of Germany at a dinner: ‘The gospel that emanates from your Majesty’s sacred person, etc.’.
1914		Lincs. Echo 22 Sept. 2/4: The German Gospel. Dr. Lenard, Professor of Physics, at Heidelberg. has issued a violent pamphlet against England, entitled, ‘England and Germany the Tune of the Groat War’.
1989		H. Rawson Dict. of Invective (1991) 171: Later generations produced such unflattering references as German comb, the fingers, [...] German gospel, boasting.

(orig. gay) the glans penis.

1972		B. Rodgers Queens’ Vernacular.
1986–7		Maledicta IX 56: German helmet n [R] Glans penis; homosexual slang.
2015		I. Welsh Decent Ride 159: Ah’m [...] pittin my boaby intae [the water]. Jist gittin it aw clean under the Jerry helmet.

(gay) amphetamines, esp. Methedrine, a German invention.

1972		B. Rodgers Queens’ Vernacular 95: German marching pills (kwn Texas, late ’60s) amphetamines, especially methedrine.
1986–7		Maledicta IX 56: German marching pills n [R] Amphetamines esp. methedrine; homosexual slang.

(US) to perform oral sex.

1992		Bentley & Corbett Prison Sl. 63: Polish the Old German Helmet Oral sex.
2003		‘Maureen’s Lusty Confessions’ on Apartment 231 🌐 My head is spinning at the mere thought of you hungrily feasting like a famished orphan on my sushi taco. Once you are finished eating my flowers way down south in Dixie, it will be my turn to polish your old German helmet...
2007		T. Dorsey Hurricane Punch 129: That slang’s possibly offensive [...] I’ll use ‘spank the monkey’ or ‘burnishing the German helmet.’.