I took a moment to look up the "what not to post" guidelines for flickr.
* Don’t upload anything that isn't yours.
This includes other people's photos, video and/or stuff you've collected from around the Internet. Accounts that consist primarily of such collections may be terminated at any time.
Sounds reasonable enough.
* Don’t forget the children.
Take the opportunity to filter your content responsibly. If you would hesitate to show your photos or videos to a child, your mum, or Uncle Bob, that means it needs to be filtered. So, ask yourself that question as you upload your content and moderate accordingly. If you don’t, it’s likely that one of two things will happen. Your account will be reviewed then either moderated or terminated by Flickr staff.
Don't tag your naked photos as work safe. Mark it as adult or you get banned. Again, it sounds reasonable to me.
* Don’t show nudity in your buddy icon.
Only content considered "safe" is appropriate for your buddy icon. If we find that you've uploaded a buddy icon that contains "moderate" or "restricted" content, we'll remove the buddy icon, moderate your account as “restricted” and send you a warning. If we find you doing it again, we’ll terminate your account.
No you cant use a macro shot of your nipple as a buddy icon.
* Don’t upload content that is illegal or prohibited.
If we find you doing that, your account will be deleted and we'll take appropriate action, which may include reporting you to the authorities.
Don't post photos of your weed grow op. The fact you'll be banned from Flickr is really only a minor reason not to.
* Don’t vent your frustrations, rant, or bore the brains out of other members.
Flickr is not a venue for you to harass, abuse, impersonate, or intimidate others. If we receive a valid complaint about your conduct, we’ll send you a warning or terminate your account.
No trolling and watch your language in comments.
* Don’t be creepy.
You know the guy. Don't be that guy.
Just because you saw a photo of a beautiful naked woman, doesn't mean she wants you to send her a naked picture of you. It will get you banned.
* Don’t use your account to host web graphics like logos and banners.
Your account will be terminated if we find you using it to host graphic elements of web page designs, icons, smilies, buddy icons, forum avatars, badges, and other non-photographic elements on external web sites.
Flickr is not a webhost.
* Don’t use Flickr for commercial purposes.
Flickr is for personal use only. If we find you selling products, services, or yourself through your photostream, we will terminate your account. Any other commercial use of Flickr, Flickr technologies (including APIs, FlickrMail, etc), or Flickr accounts must be approved by Flickr. For more information on leveraging Flickr APIs, please see our Services page. If you have other open questions about commercial usage of Flickr, please feel free to contact us.
You may not use Flickr as a product menu.
You know what. I'm totally fine with those reasons for banning people, and will continue to pay Flickr $24 a year.