Haha. I've not seen those, but I immediately want one.

I like the "I can read with my eyes shut" bookmarks :)

I'm not sure "I can do this with my eyes closed" is specifically a childlike expression? I think it's quite commonly used to say that you know how to do something very well. For something that has become second nature to you. - "Do you need a hand with that"? - No, I'm fine thanks. I've done this a million times. I could do it with my eyes closed".

It means "I can write very much better than he can." And the subtext, probably, is "So give that large contract and advance payment to me [and not to Jack]. " It mixes a couple of fairly child-like idioms to achieve this. "I can do it with my eyes closed" is a fun, or boastful, or childlike way of saying that I can do something very easily. And "you can play somebody off the park" is from the world of sports, where it is used to mean that you are a very much better player than the other person. The writer here has combined these two usages. " I can write him /// adapted sports metaphor - "off the page" //// childlike boast "with my eyes closed." I hope this helps. https://dictionary.cambridge.org/dictionary/english/with-your-eyes-closed-shut https://languagecaster.com/weekly-football-phrase-to-play-off-the-park/