This is why the male proboscis monkey has earned the nickname "Darwin's Dong-Face".
It's entirely possible that Q*Bert uses his nozzle to attract females of his species. However, given that there exists no Ms Q*Bert in the official Q*Bert canon, you can probably rule this out. What's more, were he to try waggling his nozzle at females in the human world all he'd likely receive is a police caution.
Unfortunately, Q*Bert doesn't have a visible gob, and the stumpy nature of his flaccid nozzle doesn't imply a great deal of flexibility. An elephant's trunk is also used for general grabbing, breathing, and making noises. No doubt Q*Bert breathes through his nozzle - and certainly uses it to issue profanity - but its secondary use as a prehensile tube can be ruled out...
...Or can it?
A tapir's nose is essentially a substitute hand, grabbing leaves and shit off of bushes. Again, there's seemingly nothing particularly prehensile about Q*Bert's nozzle, but perhaps he's quite good at sucking up things through it. Or maybe it works like a Dalek's sucker arm.
Elephant seals use their massive snouts to make a loud roaring sound. The louder and more sexy the noise, the more girlfriends they get. Can you imagine Poldark doing that? Or, indeed, Q*Bert? The only things Q*Bert is capable of roaring are swear words - and that seems more likely to discourage potential mates. Unless they're working class.
That may seem unlikely, but acanthocephalan has something important in common with Q*Bert: they both lack a mouth or alimentary canal. Acanthocephalan feeds off of nutrients which have been ingested by its host.
Furthermore, the canals of the proboscis open into a circular vessel which runs round the parasite's base. From the circular canal, two sac-like projections called the lemnisci run into the cavity of the body, alongside the proboscis cavity.
Each consists of a prolongation of the syncytial material of the proboscis skin, penetrated by canals and sheathed with a muscular coat. These act as reservoirs into which the fluid, which is used to keep the proboscis "erect", can withdraw when it is retracted, and from which the fluid can be driven out when it is wished to expand the proboscis.
Coincidence? Unlikely. Might we find a wild Q*Bert hanging around in the stomachs of larger animals, such as whales, gorging on semi-digested krill, using his erect proboscis?