Put ‘Er There!
Have you ever been caught in an awkward high-five situation? Of course, you have. All of us have. It’s extremely embarrassing for everyone involved, but at least you can relish the fact that you didn’t do the awkward high-five with your SO’s dad, unlike the poor OP of this story.
From across the room, he saw his GF’s dad waving at them, but for some strange reason, he took the wave to mean that he wanted a high-five. Never assume that your GF’s dad wants to high-five a total stranger. At the very best, he’ll give you the stink eye until you leave their property and never return again.