$ sed -n '6!p' filename
The above command will print all lines in filename except line #6.
The key component that makes this possible is the exclamation point (!).
Try the command on a filename containing the following content:
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8
line 9
line 10
Trevor "Red Hat Evangelist" Chandler
