nourish a viper in one's bosom

/N ER1 IH0 SH AH0 V AY0 P ER0 IH0 N W AH0 N EH0 S B UH0 Z AH0 M/
verb
  1. 1

    (idiomatic) To do acts of kindness that will be met with ingratitude and will cause one harm in the end.