Lächerlich hast du dich aufgeschirrt für diese Welt.
A ridiculous way you have girded yourself up for this world. [Kaiser/Wilkins]
You have girded your loins in a most laughable way for this world. [Hofmann]
Is this an aphorism or only a bit of wry self-deprecation? It's interesting to note that in both cases the translators felt obliged to add the word way, making the manner of the girding into the topic, rather than the girding itself. This would mean that there is a non-laughable way to gird yourself up for this world.
Girding up, protecting yourself. Is this laughable because it's been badly done, or because you're fooling yourself, imagining that you can get through life without pain, or at least without serious injury?
I think the gist of this is self-reflexive; look at how you see yourself as separate from the world, standing off to the side in a little sanctuary, readying yourself to go out and face life like a soldier strapping on armor. It isn't clear from this, though, whether the problem is a mismatch between the attitude and the one taking it, or the attitude alone. Is it ridiculous for someone like Kafka to come at life this way, but not for someone else? Or is it always ridiculous? In the first case, this is an objection intended to restore someone from delusion to self-knowledge, while in the second case, this is a comment about life.