There are many foreigners in the 'escort' business in Bangkok, Pattaya, Chiang Mai etc who are of legal age, who have valid passports to prove it but whose VISAS are expired. If one of them is found with you in your room or, say, in your car or on your motor bike, it would seem to me that the same consequences could result as those described by "billhouston" above. A hotel situation would be different in that the onus to grant admission or not shifts to reception.
Would there not be dire consequences also for bars who have foreigners on the premises without work visas? I have never heard of such an outcome in either case. Just thinking.