“Mom, It’s MY Wedding!” is the latest collaboration between Ilene Beckerman and Michael Disher at the Southampton Cultural Center, following last year’s “Sex: What She’s Really Thinking!” In a striking similarity to that show, new ideas are not at the forefront of this script. Surprising poignancy lurks between the jokes, however, and audience members — those who have been brides, have daughters who have been wedded off, or have simply wandered into the theater by mistake — will find themselves reaching for the tissues between giggles.