Theaving gas station

I acquired a nail in my tire yesterday so I took it to a gas station before it was too flat to do anything with, and merrily hopped off to work. I got back a couple hours later and picked up the car with the spare and took the flat to a tire place to be repaired which would be ready today. Overnight a friend threw an impromptu party so I rolled up with my tripod-like car and attempt to grab the party favors I keep in my trunk. Only they're gone. The guy who replaced the flat with the spare decided that my two bottles of alcohol should count as a tip, and just forgot to mention it to me. I'm absolutely livid now, and will be making outraged complaints to the management letting them know their employee is a thief.