This sound refers to the famous 'Wassup' catchphrase that spread widely from a Budweiser ad released in 1999 and reached another wave of popularity through Scary Movie in 2000. Online, people often spell it in stretched forms like 'Wazaaaaah' to match the delivery. It stayed popular because the yell is instantly recognizable, easy to imitate, and perfect for exaggerated greetings in short comedy edits, remixes, and reaction clips across social platforms.