I remember a US Army CWO transitting through ISL. He was in the Officers' Mess bar having a bar snack lunch. He was not actually thrown out but he was asked why he was not in the Sergeant's Mess.
Another cause for confusion - warrant officers, not themselves SNCOs, use the Sergeants' Mess. When on a US base, and thus entitled to use the O=club they often chose to remain with the SNCOs.