If you fly a jolly roger and NO OTHER FLAG when entering port you will be breaching the laws of probably every maritime nation. All vessels entering port are required to request a 'free pratique' and this is done by flying the 'Q' signal flag. The courtesy ensign rules are more relaxed, but are usually observed as are the rules requiring the merchant ensign of the nation of registration being flown. Other seamen will know that you are merely creating a problem for yourself and will probably assume that you are mentally retarded.
What you do on the high seas is up to you as no one is likely to take any notice.