war of nerves

Short definition from Wiktionary

Noun

1. 1
   Warfare characterized by psychological manipulation, involving tactics intended to demoralize, frighten, and unnerve opponents in order to prompt surrender.
2. 2
   A situation in which opposed parties refrain from direct conflict but maintain a tense, contentious relationship in which each uses annoyances or intimidating psychological tactics to attempt to dishearten and unnerve the other.