Guests cringe on a couch while a bathrobe-clad homeowner clips his toenails. A couple wakes to find that another homeowner has been watching them sleep. A woman at the bathroom sink gags when she spies a bar of soap riddled with strange hairs.

With “It’s Your Vacation, Why Share It?’’ as its tag line, a new advertising campaign by the online home-rental service HomeAway depicts some of the many awkward, gross, or annoying ways this kind of shared-lodging arrangement can go wrong.

The name of HomeAway’s chief rival, Airbnb, is never mentioned, but the implication is clear.

Airbnb, in addition to aiding the rental of vacant homes or apartments, gives hosts and guests the option of renting or staying in a home — in a spare room, for instance — with the homeowner present. With HomeAway, renters get the place to themselves.

“Definitely, we’re using a different kind of tone . . . it was very important to us to be clear how we’re different,’’ said HomeAway’s chief marketing officer, Mariano Dima.

Airbnb declined to comment.

The ad campaign developed also takes a swipe at hotels, depicting a family having lunch poolside caught in the crossfire of a water-gun fight.

“I think the idea of not sharing your holiday is a simple kind of thing,’’ said Kate Stanners, the chief creative officer of Saatchi & Saatchi, the agency for the ads.

Airbnb has 2 million listings worldwide, according to its website, versus HomeAway’s 1 million-plus. Several smaller companies also compete in this market. In a November research note, Morningstar analysts estimated that HomeAway had about 40 percent of the online vacation rental bookings market.