I don't get the objection:
1) If you use this as a oneliner you type as you go and the oneliner is forgotten after you use it (getting it back from your history is a possibility).
2) If this is used in a script: A comment above the command should solve the forgetting part.
Anyway, here's another solution (but more typing...
egrep -v "^[[:space:]]*$|^#" lines.txt