This question came up in Principles of Biology today, which is a valid question in getting bearings on where living things stand on the “alive scale”. I found my advisor’s response elegantly simple (which I paraphrase):
Viruses are either DNA or RNA encased in a ball of proteins with no metabolism. Sperm are more complex with cellular compartments, but the key piece in defining their alive status is that they have very high metabolic rates, consuming food to make energy (via mitochondria, like all of our other cells).
If you’ve never considered viruses as balls of protein with some form of nucleic acid inside, or that metabolism is a life-defining feature, thank the inquisitive minds of college students in 200 level biology.