I'm not sure if this will force a revision, but it was actually Uvenk of Clan Gatatog who ends up getting headbutted not once but twice before getting killed when he tries to dragoon Grunt into joining his clan as little more than hired muscle. Though admittedly, on Tuchanka, challenging either Wrex or Shepard over being headbutted would be legally classified as "suicide."

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CdrMike, Overwatch Reject