1) Attack surreptitiously 2) Bitch 3) Complain 4) Kick 5) Kvetch 6) Plain 7) Quetch 8) Say mean things 9) Sound off 10) Talk nasty about an absentee 1) Defame 
• (v. i.) To censure or revile the absent. • (v. i.) To wound by clandestine detraction; to censure meanly or spitefully (an absent person); to slander or speak evil of (one absent).
Back'bite` intransitive verb To censure or revile the absent. « They are arrant knaves, and will backbite . Shak. » Back'bite` transitive verb [ 2d back , noun + bite .] To wound by clandestine detraction; to censure meanly or spitefully (an absent person); to slander or speak evil of (one absent). Spenser. 
[v] - say mean things
bitch verb say mean things