Final answer:
Rifampin, a rifamycin class antibiotic, can cause red-orange discoloration of body fluids as a peculiar side effect, which is harmless but notable for its unique appearance.
Step-by-step explanation:
A peculiar side effect (SE) of rifampin, a semisynthetic member of the rifamycin class, is that it can cause a red-orange discoloration of body fluids, including urine, sweat, saliva, and tears. This is harmless but may stain clothing and contact lenses. Rifampin works by blocking bacterial RNA polymerase activity, thus inhibiting transcription in bacteria. Unlike more commonly anticipated side effects such as dizziness, fever, nausea, and headache, the discoloration is notable for its unusual appearance and the potential alarm it may cause in patients unaware of this effect.