Inevitably, not all goes according to plan, and the pair’s first few rendezvous are beset with hiccups and hurdles, ranging from laugh-out-loud cartoon violence to genuinely touching interludes and the blossoming of an unlikely friendship.

In the latter respect, the script, co-written by director Gene Stupnitsky, aims to pivot from broad humour to a reflective coming-of-age story where both leads learn more about themselves.

The lazy innuendo of the film’s title doesn’t do it any favours, nor does the fact Feldman looks considerably younger than 19, but there are at least attempts, albeit brief ones, to question the morality of Maddie’s task.

She seeks the counsel of her best friends (strong, wisecracking support from Natalie Morales and Scott MacArthur), but ultimately decides reward trumps any reticence she might harbour.

Stupnitsky has previous form for seemingly shallow (anti-)heroines, his screenplay for 2011’s Bad Teacher casting Cameron Diaz as a manipulative educator employing fair means or foul to raise money for breast enlargement surgery.

Here, however, the protagonist is arguably less mercenary, but it’s to Lawrence’s credit her character sidesteps tart-with-a-heart-of-gold clichés.

The four-time Oscar nominee, in her first headlining out-and-out comedy role, gives raunchy Maddie a grounding and substance the likes of, say, Amy Schumer (to whom Lawrence bears a passing resemblance) might struggle to achieve.

Her pithy putdowns in exchanges with boorish former beaus are a delight, she attacks the physicality of pratfalls with aplomb, then leavens the plot with thoughtful, dramatic reserve.

She’s matched most of the way by Feldman as the naive Percy, achingly funny when startled by the clattering of balls on a pool table or taking his first sip of alcohol, and heartbreakingly vulnerable as he sings a piano-ballad arrangement of the upbeat 1980s Hall & Oates hit Maneater (an unexpected showstopper).