The moment you realize the real reason they invited you to go camping with them.  They needed someone to service them while they spent the weekend away from their girls. Men, like them, can’t be expected to get horny and frustrated, just because there are no chicks around to bang.  You have holes that can be put into service, keeping these studs satisfied. Besides, with you they can be a rough as they want and there is no need to use condoms.  They can blow load after load of hot, thick cum deep into your guts, with no need to worry about how you feel or even if you want it to happen. After all, the three of you instinctively understand that there is no way you would even try to say no to them, especially once they dropped their pants and showed you the size of their cocks.