the commonly enjoyed act of copulation
between two exes, regardless of how messy the break up
was. Usually kept in secret (from friends and family), exsex has pros and cons: you don't have to wonder if the sex will be great or not, what partner enjoys most, or that you are sleeping with too many people. Cons are feeling dirty afterward, possibly contracting an std from your lying whore
of an ex, or eventual emotion attachment and later probably shut down that some (very few) people feel during or after sex.
Man, I had exsex with Dave last night, it was awesome, but I don't think it was a good idea, I definitely need to shower in scalding hot water and then go to the STD clinic and get tested.