It may have been inspired by the real sightseeing, enough to be put in verse - apparently, this endearing saying was put into iambic senarius.
(CIL IV, 4488)
98) CIL IV.4488 (iambic senarius) [House VI.13.19] [Courtney #82; Spal #15]
seni supino — sympathetic dat. (see ad 1824) supino — pred. (“when he is lying on his back”) colei — (pl.) scrotum [Adams 1982: 66-67] [trisyllabic]
[A rather unhappy image that recalls the Grk. λακκοσχέας (“man with hanging scrotum”), suggesting either profligacy (cf. Latin ecfututus) or, as here, the impotence of old age. The condition can be caused by a varicocele, which is mocked in the elderly at both Lucilius 331-32 and Juvenal 10.204-06.]
[This piece suggests that, like the Greeks, the Romans idealized the compact genitalia of the young man who was just coming of age (Grk. ephebe). The allusion to the man’s anus has no practical purpose but merely enhances the description’s gross specificity. (For a modern comic treatment of this theme, see Ricky Gervais, Humanity [2018] at 49:26 minutes.) Spal suggests that the piece might have been motivated by other nearby graffiti that have a distinctly homosocial cast and offers useful comments (153) re the manner in which it employs the form of a traditional maxim to challenge the reader to provide an interpretation.]
[Shackleton Bailey’s interpretation (Phoenix 32 [1978] 321-22) seems somewhat overly involved: “An old man, qua cinaedus, is undesirable, and, when lying on his back, inaccessible. All his colei are good for is to offer a protection which his culus does not need anyway, i.e., they are good for nothing.” Contrast Rhode (cited by Wick 222): “Eines Kommentars bedarf wol dieses freilich nicht besonders appetittiche Bild eines zuruckgelehnt (wol betrunken) daliegenden greisen λακκοσχέας nicht” (loosely: this grotesque image of a naked [and no doubt drunk] old man requires no commentary).]
From: A Sampling of Graffiti and Other Public and Semi-Public Texts from Pompeii and Herculaneum