If you wear that silly costume, you will be a laughing stock.
laughing stock
idiomAn object of ridicule, someone who is publicly ridiculed; the butt of a joke.
Origin
disputed originFrom laughing + stock (“source, supply; butt, target”). Compare also whipping-stock, jesting-stock.
After his failed presentation, he became the laughing stock of the entire office for weeks.
The politician feared that his public blunder would make him the laughing stock of the nation, effectively ending his career.