It means not worth mentioning. Ex：这件小事虽然看上去微不足道，但是却对整件事情的发展起到了重要的作用。 This incident seems not worth mentioning, but it plays an important role in the whole thing.

"微不足道我懒得杀你。" Shall I assume that the preceeding sentence means something like: "I'm too tired to kill you now, you don't need to thank me" I think the speaker intends to be sarcastic

that means something is too unimportant to talk about. eg.个人的力量与集体的力量相比是微不足道的。

It‘s a proverb.微：细(thin)，小(small）；足：值得（worth）；道：谈起（talk about）。微小得很，不值得一提。not worth mentioning;cut no figure e.g.The peasant laboured for a mere pittance.农民仅仅是为了微不足道的收入而辛苦地劳作。

Small pretty, not worth mentioning. Meaning, value was not worth mentioning.