Revenge of the Nerds II
Nerds in Paradise
(1987)

Lewis (Robert Carradine) and the other nerds are stranded on an island along with Sunny (Courtney Thorne-Smith).  The discover a cache of artillery including a tank and use it to return to Fort Lauderdale in time for the fraternity vote.  Just before the Tri-Lambs are voted out, the tank busts through the wall.  Lewis confronts Roger (Bradley Whitford) and Roger admits to setting the nerds up to make it look like they stole his car.  Lewis punches him into the pool and the nerds are the heroes again. 

Thanks DrummerBrian!