A possible concise summary is:
Marvin and his family go to the beach, where his wife's ex-boyfriend Brad saves their son Jeffy from drowning. Marvin's wife invites Brad to dinner as a thank you, but Marvin is jealous and tries to sabotage the food with Chef Pee Pee's help. Brad chokes on a shrimp and appears to be dead, but he is revived by Chef Pee Pee who is disguised as a doctor. Brad reveals he has a shellfish allergy and a surfboard stuck to his hand.
Here are the key facts extracted from the text:
1. Marvin and his family went to the beach, but Marvin did not want to go.
2. Jeffy almost drowned in the water, but he was saved by Brad, who is Rose's ex-boyfriend.
3. Rose invited Brad to dinner at their house as a way of thanking him.
4. Marvin paid Chef Pee Pee to make the food disgusting so that Brad would not like Rose.
5. Brad choked on a shrimp and appeared to be dead, so Marvin and Chef Pee Pee tried to get rid of his body with acid.
6. A cop showed up looking for Brad, who turned out to be alive and had a shellfish allergy.