ber ‧ serk /bɜːˈsɜːk, bə- $ bɜːrˈsɜːrk, ˈbɜːrsɜːrk/ BrE AmE adjective
[ Date: 1800-1900 ; Language: Old Norse ; Origin: berserkr 'wild fighter' , from björn 'bear' + serkr 'shirt' ]
go berserk informal to become very angry and violent:
Dad went berserk when he found out.