All of my immediate family knows I bet on games. Many members of my extended family know or definitely suspect (they likely know I have some kind of financial interest, but might be surprised I'm literally placing straight wagers with a bookie and not just in some pool or betting with a buddy or something).
What always gets me is the uncle/cousin/in-law that "knows", and kinda tries to be "hip" about it, but can't for the life of them understand a point spread.
Them: "Who you got on this game?"
Me: "Notre Dame"
Them: "What's the bet?"
Me: "ND -5"
Them: "So wait...if they lose you lose?"
Me: "Yep"
Them: "So if they win by 3 you win?"
Me: "No. They have to win by at least 6"
Them: "But if they lose by less than 5 you win right?"
I've tried explaining it so many different ways.
"ND is -5"
"ND has to win by 6 or more"
"Take ND's final score and subtract 5 from it, and that's my score"
"ND is favored by 5"
Some people just can't grasp it. And don't even get me started on trying to explain moneylines.
Typically these days I'll just say "Yeah I have ND, they just have to win"