That '70s Show S04 E21 Prank Day

"Be groovy... be very groovy!"

It's Prank Day according to Kelso, who manages to trick his friends twice with his stunts. The guys' attempt to retaliate backfires horribly when Red triggers their prank instead. But rather than venting his wrath on Eric, Red joins the prank war to show the boys how it's done. Meanwhile, Jackie throws an impromptu slumber party to cheer Donna up on her parents' wedding anniversary.