Expanding on a previous post...
SSC - Safe Sane Consensual
RACK - Risk Aware Consensual Kink
PRICK - Personal Responsibility Informed Consensual Kink
CCC - Committed Compassionate Consent (implies a longer term connection)
Everything we do in life, not just BDSM, carries a risk assessment and calculation, with that, analyze the risks of things, look to manage and mitigate the risks and choose for ourselves if the reward for taking the risk is worth it or not.
So where is 'the line'? It really depends on the people involved! Trust is a huge part of the deal.