vexatious

Short definition from Wiktionary

Adjective

1. 1
   Causing vexation or annoyance; teasing; troublesome.
2. 2
   Full of trouble or disquiet
3. 3
   Commenced for the purpose of giving trouble, without due cause.
4. 4
   In the habit of starting vexatious litigation and therefore liable to have restraints placed on one's ability to access the courts.