1. superlative form of goofy; most silly, foolish, or ridiculous in behavior or appearance
Usage: informal; commonly used in casual speech
2. superlative form of goony; most resembling or characteristic of a goon; most thuggish or brutish
Usage: informal; less common than the 'silly' sense

Examples

• He made the gooniest faces during the entire comedy show.
• That was the gooniest dance move I've ever seen at a party.
• She wore the gooniest outfit to the costume contest and won first prize.
• The gooniest character in the movie always got the biggest laughs.
• His gooniest impression of the teacher had everyone in stitches.
• That's the gooniest thing you could possibly say right now.