Drinking excessive amounts of alchohol are never good regardless if you have MS or not. If you take certain medications, then you should not drink alcohol at all. Talk to your doctor to more specific information.
Some people with MS have heat sensitivities (like me). When the body overheats, the nerves transfer signals more slowly and your MS symptoms may become more noticeable. When this happens, it is called a pseudoexacerbation and doesn't cause any permanent damage.