Green’s Dictionary of Slang

lob n.³

the penis, esp. when half- or fully erect.

1896		Farmer Vocabula Amatoria (1966) 46: Boyau ridé = a worn out penis; ‘a lob’.
1925		E. Field ‘A French Crisis’ in Facetiae Americana 20: Let other kingoes, lobs and yards, in adoration drop.
1964		H. Selby Jr Last Exit to Brooklyn 47: Harry [...] tolder he got a nice fat lob forer ta suck.
1972		B. Rodgers Queens’ Vernacular.

In compounds

lob-on (n.)

an erect penis.

2024

S. Kempner X 2 July 🌐 I love seeing Tories lose seats but I hate seeing Starmer with a lob-on.

In phrases

on the lob (adj.)

of the penis, semi-erect.

1896

‘Farmer’s Daughter’ in Cabinet of Venus 80: His staff was [...] on the lob, in a sort of ‘half cock’.