Do you make bets with your friends?
I do, from time to time. My most recent experience about this kind of situation with a friend was the EFL cup final between Liverpool and Chelsea. Being a Liverpool fan, I was of the opinion that Liverpool would win the tie but my friend thought his team would win so we entered took a bet against each other. There are other experiences — this was the most recent.
It's a completely normal one. Most times, it's even fun and can score you some bragging rights if you're lucky enough to emerge the winner. As with all bets/gambles, one should only enter into a bet with an amount they'd lose without problems.