I had my first guy try to do some anal play while giving me oral within like the first 3 times. First boyfriend to do oral with, and I was already kinda iffy about that (just the idea of receiving oral, not "this is going too fast" type deal). When he tried it I had to just stop him and tell him no. He was pretty understanding.
Now I'm comfortable with the idea of anal. I think my opinion of it would be ruined if I had let him try it, though.
My current guy has not suggested anything I'm uncomfortable with so far.