Cheech and Chong, Harold and Kumar, meet your natural heirs Jessie and Angela. In the raunchy, funky, flaky and fairly hilarious "Never Goin' Back," they give stoner friendship comedies an unexpectedly sweet salute to teenage sisterhood.

Augustine Frizzell, an actress, art director and costume designer, makes her writing/directing feature debut a dumb-and-dumber, high-and higher hoot. There's a wobbly line between amiably wacky and annoyingly lazy, but Frizzell stays on the right path. Missing this delight would be downright disgraceful.

This is a story where baked brain cells come from many sources. It's set in a nameless Texas small town where the summer breezes are about 98 degrees in the shade. It's so sweltering that Angela (Maia Mitchell) and Jessie (Camila Morrone), roommates and BFFs, want nothing more than to escape to somewhere cool and open.

Angela, the planner of the pair, arranges a 17th birthday surprise for her bestie, a getaway trip to Galveston. It's no tourist mecca, but it's got beaches and supercheap fares they can afford by pulling 10 extra shifts at their waitressing jobs at the diner. And until their getaway, they can go to the grocery store, open one of the big doors in the freezer section and hold up their hair while they cool their backs.

Handled wrong, a story about two minimum-wage high school dropouts would not be the material for a good time. But this goofball coming-of-age story has a childish, fun-addled sense of invulnerability. It's loose and playful in a way that studio movies rarely achieve. (Frizzell is married to indie maverick David Lowery, which may or may not have something to do with her attitude.)

The plotting is a "really, OK, whatever" mess, but there's hardly a shaggy moment to miss. As a weeklong string of setbacks put their semi-organized vacation plan in danger, you hope these soul mates can somehow glue it back together. And the worse their recovery plan, the more you want the adorable lunkheads to succeed. This is the kind of movie where every setback and questionable decision has a silver lining of inane "Napoleon Dynamite" comedy or an in-your-face gross-out gag.

The girls' housemates are Dustin (Joel Allen), who's Angela's criminally incompetent wannabe drug dealer older brother, and Brandon (Kyle Mooney from "SNL"), a rumpled, alienating drip who hopes to seduce the ladies to take a ride on "the Brandana," though the odds of anyone agreeing to do that are incalculable.

The key to the film is the pinkie-promise friendship between the lead characters, which Morrone and Mitchell perform with enough electricity to run a power grid. Their scenes together are inspired, and they are clearly having fun nonstop. They are never separated for a single scene, whether they're doing hip-hop karaoke in a friend's car, planning a hair-brained heist or showing up for work off-the-scale stoned.

Mitchell (TV's "The Fosters") makes Angela a kindhearted idiot savant who's scrappy as a wolverine when peeved. As Jessie, Morrone ("Bukowski") has a magnetic charisma as she radiates a quality of irresistible, innocent-as-a-puppy friendliness. Their characters are scattershot, undisciplined, inspired and entirely lovable, as is the film.