I'd say 'armselig' would be a better translation for 'pathetic'. The first word that comes to my mind when hearing 'lächerlich' would be ridiculous. But maybe that's just me?

I agree that "armselig" is a more suitable translation in a lot more cases than "lächerlich". But this translation clearly carries the meaning #3 in the M-W reference and the sentence "This is pathetic" as I have heard it used from Americans carries meaning #4 to a larger extent than #3 (although this is implicit as well).

Online Etymology Dictionary
Meaning "arousing pity, pitiful" is first recorded 1737. Colloquial sense of "so miserable as to be ridiculous" is attested from 1937.
http://www.etymonline.com/index.php?term=pathetic

Stimme auch für den Eintrag.

pathetic, ridiculous, silly:
inspiring scornful pity; "how silly an ardent and unsuccessful wooer can be especially if he is getting on in years"- Dashiell Hammett
(WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved.)
pathetic, ridiculous, silly is similar to:
* undignified — lacking dignity
http://www.answers.com/topic/pathetic-ridicul...

Synonyms for pathetic (adj):
ridiculous {adj}
silly {adj}
--
pitiable {adj}
pitiful {adj}
--
hapless {adj}
miserable {adj}
misfortunate {adj}
piteous {adj}
poor {adj}
wretched {adj}
© Princeton Univ.
http://www.dict.cc/?s=pathetic

Pons Wörterbuch der Jugendsprache; online:
Fruchtzwerg der (lächerliche Person) pathetic person
spackig adj (lächerlich) pathetic, laughable
http://www.englisch-unterricht.maxdsl.de/juge...

Definitiv als einzutragende Nebenbedeutung unterstützt.