The line comes from the 2014 comedy 22 Jump Street, where Channing Tatum as undercover officer Greg Jenko blurts out My name is Jeff in a strained falsetto during a meeting with gang members. The short scene was clipped and shared heavily on Vine in 2014, then spread to YouTube and later TikTok as a reaction sound. Extended and pitched versions like this jeffffff edit keep the joke alive, because the phrase works without context and can introduce any person, pet, avatar or username in a deliberately uncool way.