about your indenting: it looks like you heard the bell but are unaware of it's location ;_)

this looks a little bit more proper:

On *:Action:*Poke*:#:{ 
   if (($me isin $1-) && (%antiflood)) { 
      set -u5 %antiflood 2
      inc %Slapexx
      describe $chan slaps $nick right back %slapexx
   }
}

other than that, it seems to look fine ;_)