my favourite is "if you can laugh while others around you cry, it just means you went around the bend first and you might as well have some fun till the rest of them catch up!"
also depending on the circumstances:
"you and whose army??"
"i want to start life over under an assumed name"
"god has a nasty sense of humor"
since retired from work due to health problems "not my fault, i'm heavily overmedicated" even if i'm not that day!
and my all time, all around favourite......"OH ****!!!!!!"