AppleScript Editor : comment line shortcut?
I have used FastScripts to assign a shortcut to this script:

set text item delimiters to linefeed
tell application "AppleScript Editor" to tell document 1
    set input to its text
    set {c1, c2} to character range of selection
    if c1 is 0 then
        set {p1, p2} to {1, 1}
    else
        set p1 to count paragraphs of text 1 thru c1 of input
        set p2 to count paragraphs of text 1 thru c2 of input
        if p1 is not p2 and {return, linefeed} contains item c2 of input then set p2 to p2 - 1
    end if
    set selection to paragraphs p1 thru p2
    do shell script "input=" &amp; quoted form of (paragraphs p1 thru p2 of input as text) &amp; "
if [[ -z $(sed -E '/^[[:space:]]*($|#|--)/d' &lt;&lt;&lt; \"$input\") ]]; then
  sed -E 's/^([[:space:]]*)(#|--)[[:space:]]*/\\1/g' &lt;&lt;&lt; \"$input\"
else
  sed -E 's/^([[:space:]]*)/\\1--/g' &lt;&lt;&lt; \"$input\"
fi" without altering line endings
    set contents of selection to result
end tell