As a REAL dom I say you do not SAY anything. You get up and as quickly as you can get out of there. The person you are with is a poser or a wannabe and has no respect for you (Subs are deserving of respect, it is essential).
It is jerks like this that give us bad names. You DO have limits and they must be respected at all times. 'Soft' limits can be explored I feel after trust is built up between dom and sub and with MUTUAL consent. But even then you move very very slowly.
Hard limits are HARD limits, not to be breached.
RUN! :-)
And Pardon me for encroaching on the sub, um, 'space.'