If you really want to get under a criminalists skin, call them a criminologist. The two terms are not interchangeable. Criminologists study criminal behavior, causes, and control as it relates to culture and society. They study things like recidivism rates, socio-economic stressors on criminal behavior, and the consequences of criminal activity on society (to name a few). You won’t find them at active crime scenes or working in a crime laboratory. Typically you’ll find them in Universities, independent academia, and non-governmental organizations (NGO). Think of them as cultural or behavioral scientists (not a great description but for our purposes it works).
Criminalists on the other hand are physical scientists who use scientific methods and techniques to find and interpret physical evidence. This includes DNA, blood, fingerprints, ballistics, etc. We rely on scientific findings and techniques used in a particular field and apply them within a legal framework. For example, the methods used by a forensic entomologist are the same used by a medical entomologist, just applied to a criminal investigation.
Accurate descriptions are important. They tell the informed audience that you have done your basic homework. In contrast, calling a criminalist a criminologist knocks you down a few pegs on the ladder of credibility with those knowledgeable of the fields. It is an easy mistake to make and an easier one to avoid.