Sometimes it would be helpful for me if PopClip doesn’t appear when I make a selection, such as when I’m working with someone and want to highlight something we should be looking at together (i.e., when it would be distracting if PopClip appeared).
Was there a plan to have a modifier key act as a show/don’t show trigger?
Like holding down the option key while making a selection = don’t show PopClip.
I kind of recall this coming up before, but wasn’t able to find a post about it. 
Not sure whether there’s a shortcut that prevents PopClip from showing up but you could use ESC to hide it.
This already exists, but the key to hold is command (⌘).
The fn key works too.
… By the way, a reason it’s not ⌥ is that you can ⌥-drag to select the text of a hyperlink, instead of dragging the link as an object. So it’s useful for PopClip to still appear with ⌥. And it’s not ⇧, because that is used for making text selections by clicking. And ⌃-click pops up the context menu. So it’s ⌘ by elimination.
Also, ⌘ is nice because if you are planning to press ⌘C anyway, then having ⌘ already held down will suppress PopClip from messing up your ⌘C.
Aha! Beautiful! Sorry I missed/forgot it! 
No worries! I’d generally rather people ask than suffer in silence.