Thanks to Steven Novella at neurologica/SBM, though I have seen this one before somewhere. Another tool in the argument box I need to start keeping.
"You can't prove it's false -> absence of evidence is not evidence of absence."
I have had this one used on me before. It's not actually try though. Or rather it's only true as a universal. As a local statement, it can be but is not necessarily true. For example, "There is an elephant in my house". I search my house looking for an elephant and find no evidence for one. At which point in time I can pretty conclusively say, there is no elephant in my house. In which case absence of evidence is evidence of absence.
If you want to be reeeeally picky, technically I might have a mental disorder that prevents me from seeing elephants in my house. In which case absence of evidence is still pretty good evidence of absence. It might not be proof of absence, but it's pretty good evidence. And I would probably still draw the conclusion that there are no elephants in my house.