In How I Met Your Mother Barney lost the Slap Bet some time ago. Being a somewhat inconsistent viewer, I can't recall the episodes that fulfilled the bet, and in my mind, at least 1 is still due. What is the count outstanding on this?
In "Slap Bet" (Season 2 Episode 9) Marshall was granted 5 slaps to be delivered any time in the future without warning.
5 + 3 = 8
out of which
slaps have been executed.
The 1st slap was executed in "Slap Bet" (Season 2 Episode 9)
The 2nd slap was executed in "Stuff" (Season 2 Episode 16)
The 3rd slap was executed in "Slapsgiving" (Season 3 Episode 9)
The 4th slap was executed in "Slapsgiving 2: Revenge of the Slap" (Season 5 Episode 9)
The 5th and 6th slap were executed in "Disaster Averted" (Season 7 Episode 9)
Hence, there are
2 slaps remaining.
On a related note, the 7th slap has a countdown at Slapbet Countdown! :D
Update: Both those slaps were delivered before the ending of the show.
According to the How I Met Your Mother wiki, the original five slaps have all been used. However, Barney offered Marshall another three as payment on a separate bet, one of which has been used. Two remain as of this date.
All slaps were used.
In season 7 episode 9 "Disaster Averted" Barney managed to get Marshall and Lily to agree to 3 additional slaps in exchange for letting him take the Ducky Tie off. Marshall then had a total of 4 slaps which he proceeded to use 2 right away. This left Marshall with 2 slaps.
Then is season 9 episode 14 "Slapsgiving 3: Slappointment in slapmarra" Marshall told the story of how he learned the slap of a million exploding suns in an attempt to scare Barney. He slapped him under a tree next to four women and a tiger.
The last slap took place in season 9 episode 22 "The end of the aisle". Towards the end of the episode while Barney waits for Robin to walk down the aisle, Barney starts to freak out again so Marshall slaps him thus freeing him from the slap bet.