Back in the old days folks would go to the drug store and sit at the bar for "seltzer water" mixed with different herbs and extracts thought to give medical properties, this seltzer water was also known as "soda water" or "soda pop" due to the carbonation and bubbles it produced. This in time was shortened to just "pop" or "soda" in different areas.
The pharmacists grew tired of mixing these libations themselves so they hired men to take over this job, they were referred to as "Soda Jerks".
Calling all carbonated beverages "coke" is just ignorant, and I have never heard of that before.
Mystery solved:
http://en.wikipedia.org/wiki/Soda_jerk
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