I think - and plenty of people on the server agreed with me - that your spray was, while hardly hardcore pornography, beyond the bounds of what we wanted to see in our cartoon game of a friday evening. NSFW literally means that - would you set that as your work computer's desktop wallpaper?
That's beside the point, though: you don't need a fine-grained definition of what is unacceptable because I told you that that specific thing was. Several times. When an admin tells you not to do something and you do it and then run away giggling, expect to recieve, as phi put it, a slap on the wrist.
I'm glad to hear you won't be doing it again: continuing would lead to longer bans.