The bar for teen-sex comedies has never been very high, but this one clears it and then some. A high school virgin in the Chicago suburbs (Josh Zuckerman) steals his brother’s vintage Pontiac GTO and, accompanied by two pals (Clark Duke and Amanda Crew), sets off for Knoxville to meet an online girlfriend who’s promised to initiate him sexually. The gags are as idiotic as you’d expect, but they consistently hit the bull’s-eye (as part of his after-school job, the hero patrols the local mall in a giant doughnut costume, unaware that pranksters have appended it with a big dildo). There’s also a very funny extended sequence at an Amish farm where the tradition of rumspringa—allowing adolescents to sample mainstream morality—leads to a crazed, bacchanalian barn party with live music by Fall Out Boy. Sean Anders directed, and Seth Green contributes a cagey performance as a jaded and sarcastic Amish farmer. R, 109 min.