get (one's) claws out

1. Literally, of an animal, to prepare for an attack or for defense by protracting or displaying its claws. I hate my neighbor's cat, it always gets its claws out when I go near it.

2. By extension, to become particularly aggressive, especially in preparation for a confrontation. (Most often said of a woman.) Jenny had her claws out after she found out Mary had been spreading rumors about her in school.