He's too damn old for an accidental mating bite.
"Call them accidental one more time," Crowley says, "and I'll kick you off the bed."
"It's my bed," Bobby mutters at him, "and you'd be back to begging for my knot in minutes flat." Just to prove his point, he wrestles Crowley ass up again, grinding his cock against his heat-soaked hole until Crowley whines—turns out demonic Omega noises make Bobby dizzy, not that he's complaining too much—and he sinks back in where Crowley's loose and easy from a good knotting earlier.
Accidental, definitely, but… he's not really regretting it now.