I ran up like a $5k bill over a couple weeks by having an application log in a hot loop when it got disconnected from another service in the same cluster. When I wrote that code, I expected the warnings to eventually get hooked up to page us to let us know that something was broken.
Turns out, disconnections happen regularly because ingress connections have like a 30 minute timeout by default. So it would time out, emit like 5 GB of logs before Kubernetes noticed the container was unhealthy and restarted it, rinse and repeat.
I know $5k is chump change at enterprise scale, but this was at a small scale startup during the initial development phase, so it was definitely noticed. Fortunately, the only thing that happened to me was some good-natured ribbing.