I once replied "STOP" to a text-alert system I'd just been coerced into joining, and immediately received another text saying they'd stop.

The extra text really bugged me at the moment. Using iMessage through my desktop, I spammed "STOP" texts to the number as fast as possible, receiving the same auto-reply each time.

I wanted to see if it would hit some limit, and after about 200 texts, I stopped receiving a reply.