Michael Idehen was caged on his 18th birthday after murdering 15-year-old Kyron Webb in a row over comments on Snapchat.
Harrowing CCTV footage showed him plunging a knife into his rival's heart in Moston, Manchester, in October last year.
The scholboy died three days later in hospital.
Idehen had previously uploaded a YouTube video of him rapping about "cheffing" – a slang term for murder.
The clip, which appeared online in August 2017, features a number of masked youths and includes the repeated rap "he backed his shank [knife], he waved it around, but he didn't do no cheffing".
He was jailed for 15 years alongside a 17-year-old caged for five after pleading guilty to manslaughter.
The other teen cannot be named for legal reasons.
Sentencing, Judge David Stockdale QC said: “Kyron had done nothing to justify, excuse or explain the brutal and cowardly attack on him.
“He offered his attackers no violence nor any threat of violence at all.”
Kyron's mum Rachel hit out at the murder in a heartbreaking poem after her son's death.
It read: “I ache in bitter sorrow as I remember my little boy. Rest easy in Angels arms, remember to look down on me. You will always be my king, my thoughts and every memories.
"I love You Kyron Antonio Webb for all eternity. I will never understand why you were taken from me.”
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