What would make my 1993 Honda Accord spark plug smell like diesel fuel?
Contaminated fuel. This is more common than you would expect. The same delivery trucks are sometimes used to transport different grades of fuel. Under normal operating procedures the tanks are flushed after each haul. This helps prevent contamination of diesel and regular grade fuels. When this step gets over looked there can be upwards of a 100 gallons being mixed in the next load.
When your fuel is contaminated the engine may struggle and have performance issues. The engine may “PING” on heavy acceleration. Though in the short term no damage should occur but if not corrected severe internal engine damage will. Feel free to drive that tank out and fill up at a different fueling station the go around. For large fuel tanks an Octane boost may be used to prevent engine ping.