@14“ I use „schieß mich tot“ differently than I would use „I can‘t remember for the life of me“.
For example, if someone asked me how much I paid for something and I couldn‘t remember (or was unwilling to give) the exact figure, but I do know approximately how much, I might say „Achtzehn Euro schießmichtot“. Or I might tell you that a certain scientific discovery was made in „Achtzehnhundert-schießmichtot“ if I was pretty sure it was in the nineteenth century but not in which year precisely. So I have an idea of the ballpark at least.
„I can’t remember for the life of me“, on the other hand, to me means that I really have no idea, so in my first example I wouldn‘t even be able to say whether it was eighteen euros and a bit or maybe only eleven euros, or even thirty euros, and in the second example I might only know that the discovery was made some time before my own lifetime, but not in which century.
Also, see #9: In such a context, „schieß mich tot“ (or „schlag mich tot“) is closer to „and goodness knows what else“ or maybe „everything but the kitchen sink“