Whenever I hear someone say something like "build up my immunity", I ask, "OK, can you explain to me how your immune system works to fight off infections, particularly those caused by viruses?", dunderheads like this inevitably spew out a load of nonsense, usually mentioning irrelevant vitamins, exercise, and with zero understanding of the actual underlying processes. If they've passively absorbed any real information, they might mention antibodies (but often get them confused with antiobiotics) or T cells, but when pressed further, they have no idea what these actually do, much less how they get selected and differientiated.
One year later and I've lost all patients with these meatheads.