Having read your reply, which, in response to my first ever post, was impressively speedy, I think I've got the gist of the sentence.
I don't know if you're allowed/encouraged to swear on this forum but my translation of the overall phrase would be:
tell [the person] to go f**k himself/eat biological products and [not do something]
Please folks do continue to reply if you have anything to add. Whether I have the gist or not, this is fascinating stuff.. Long live language forums!! I hope in the future to be able to contribute more than ask...
I believe the idea of "comerse los mocos" is that of doing nothing useful or desired (depending on the circumstances) when the circumstances demand them. For example, I remember having heard the expression with some frequency when I was a teenager in Argentina.