on :action:$($+(,slap,,$me,)):#:{
if ($me isin $1-) {
describe $chan { slaps $nick }
}
}

Rather do it this way:

on :action:$($+(,slap,,$me,)):#: {
describe $chan slaps $nick
}
OR
on :action:slap*:#: {
if ($me isin $1-) {
describe $chan slaps $nick
}
}