In sex… what is off limits?!?!?

In the bedroom, what is something you would not be willing to do?  For me, it is any type of penetration from behind (in the butt)!!!  That is a NO-GO for me.  Don’t get me wrong, I have tried it but OUCH!!!!!!!  How does you guys feel about anal sex?

What is a no-go in  the bedroom for you??