What is it called when rappers sing out of tune for effect eg jaden smith singing the lines 'got to be the best and yes you're the flyest like david and goliath i conquered the giant'?

This technique is often referred to as "melodic rapping" or "sing-rap," where artists intentionally use off-key or unconventional vocal techniques for stylistic expression. It can also be associated with "autotune" usage, where the effect creates a unique sound that emphasizes emotion or artistic identity. In some cases, it's simply an artistic choice to convey a particular vibe or mood in the music.