When will you challenge a person's religious beliefs, and when will you not?
When they try and quote the bible, then I'll start my questioning.
I can quote stuff right back that will make then Go Away! Buwahahahaaaa!
When they are using it to bully others...otherwise, not my business, nor my beliefs, theirs.
When they proselytize, then I go full atheist. Or in the case they are Christians, I can go full Christian extremist and show why he/she is a bad christian and will go to hell anyway...
But in general I never discuss in the matters of religion, i discuss in the matters of science (hard science, social sciences, history etc), if the religion contradicts or find a "cosmic nany explanation" for something, then I will challenge.