Alcohol
Worse Combination Chess and ????

For me worst combination is chess (actually playing OTB) and social interaction. Also chess and wrong time of day. Last one is more like state of mind. Sometimes I make a move in correspondence chess before going to sleep or when I wake up in the morning. Those are the times when I feel relaxed and most confident in my moves and those are the times when I make the worst and stupidest blunders.
sleep