Which of the following describes the action of grabbing someone's private parts without consent?

The action of grabbing someone's private parts without consent is best described as indecent assault. This is because indecent assault specifically involves unwanted physical contact of a sexual nature that is intended to be offensive or provocative. It acknowledges the lack of consent and involves a violation of personal boundaries in a sexual context.

While battery involves any unlawful physical contact, it may not always carry the same sexual connotation as indecent assault. Sexual assault, on the other hand, is typically understood as a broader term that may include a range of non-consensual sexual acts, including but not limited to inappropriate touching. Harassment generally covers unwanted comments or actions that create an intimidating or hostile environment but may not necessarily involve physical contact. Therefore, indecent assault is the most fitting term for the specific action described in the question.