The painful knot on your forehead that develops from repeatedly banging your head against the wall out of frustration, disbelief and/or abject horror at Trump's inability to form complete thoughts & sentences, tell the truth, treat people with respect, etc etc etc. (Basically anything he does)
"Dude, your Trump bump looks wicked"
"Yeah, I just listened to his latest thoughts on the Russian hack. I'm seeing double and have to repair the living room wall again."