Classical conditioning is when two stimuli are paired and they form a new behavior or response. The most famous example of this would be with Pavlov and his dog that everyone studying psychology has heard of at one point throughout their schooling.

I was trying to thing of a way I have become classically conditioned while I was sitting in my kitchen and my dads phone rang. I immediately had flashbacks to the feeling of waking up early in the morning and I immediately grabbed my phone to turn it off. I then realized that his ringtone is the tone I have set for my alarm.

When I was at my previous job I had to wake up every morning at 4:30 and I set this tone because it was the loudest, most obnoxious one. I did not particularly like that job so every morning when my alarm would go off I dreaded it. Now, a couple months later I still get reminded of that job and waking up early every time I hear that tone.

Cognitive Psychology Connecting Mind, Research, and Everyday Experience.  Goldstein, E. Bruce. 2011.  Third Edition.  Wadsworth, Cengage Learning.