大湿哥大湿妹
[dà shī gē dà shī mèi]
In Mandarin, '大湿' sounds quite similar to '大师' - meaning a great master. So, this user name is using wordplay to give itself an image of seniorship, respect or authority while adding in some whimsy and friendliness with the terms of address: elder brother (哥哥) or elder sister (妹妹).