thigh-slapper

The term "thigh-slapper" can be translated to Spanish as "broma muy graciosa" or "chiste que hace reír mucho," depending on the context. If you mean it in the sense of something very funny, "broma" or "chiste" captures it well. If it’s in a more humorous or informal context, you might also refer to it as "algo muy chistoso." However, there's no direct equivalent since it’s an idiomatic expression in English.