So, unless the service you received for $16 was unsatisfactory, then I can see why you feel "stupid". Maybe the waiting area was unclean. Or the bathroom ran out of TP. Maybe the TV wasn't working. Coffee machine was broken. Temperature in the waiting area was uncomfortable. And anything else that made your experience unpleasant.
But as for the $16 dollars of labor, that's really not that much. Next time, you should check your own air filter, check tire pressures, differential fluids, transfer case fluid, transmission fluid, engine air filter, brake lights, reverse lights, head lights, turn signals, test your battery, check coolant and power steering levels, etc... This is what I expect when I come in for an Oil Change and Lube.
[..snip!]
I'm at a point in my life where I feel that it's ok to pay someone else to get dirty and dispose of the oil and filter properly. I don't want to check ALL of my fluids. That's what I expect for service.