Four soft inches
There are times (oh, ok: most times) when a sex shop catalog can tell so much more than a sociology essay. Want an example? Clicking this link will get you to Mr. Limpy – which is exactly what you are thinking of: a big fake cock. Totally soft.
Who can ever want to buy an artificial erectile dysfunction? Excepting the really inscrutable cases, the answer is probably those into packing, which basically amounts to stuffing your underwear to impress potential partners.
Among lesbians this is an obviously ironic provocation that can be, in a way, somewhat sensuous; conversely, if a man does it the intent may even be sensuous, but I doubt the results can be other than irony. Either way it is quite curious that somebody invented an object reproducing the non-aroused state. Now we only have to wait for push-down bras, ass-flattening briefs and other uglyfying sex toys.