Bor is saying "WAVE AT TWING!" or more correctly/phonetically "Wav-ee at twing". Maybe it's some really old Asgardian insult, but I doubt it. Kinda killed the drama for me.
Had they gone with
then "Have at thee!" would have worked.
To be honest, I liked the idea of him speaking Norsk/Icelandic ("Bor Lifa Endr") to begin with, as it set him apart from everyone else speaking in 'runes' lately (Skrulls, Dr Strange, whoever the Hel that jerk over in Mighty Avengers was, etc).
Otherwise? It was beyond incredible and worth the wait.
"Twing" is an old Norse term for a male's genitals, and he's basically saying say goodbye to it.