Heat the margarine or butter gently until it is melted. In a medium bowl, combine the crushed pretzels and sugar with the melted margarine and mix thoroughly. Press the mixture into a 9-inch pie plate to form a crust.
In a large bowl stir together ice cream, limeade, tequila and triple sec. (Or you can dump everything into a food processor and blend for a few seconds.) Pour into the pie crust. Freeze for 4 hours or until firm.