Sounds like you have had a stinky one yourself.
You never been with a chick back in the day when things are getting hot and heavy, you guys are rubbing on each other, she is rubbing all over you, you her...so you get your hands down her pants and start playing with the poo nanny a bit. She seems to like it and you think you may want to munch on a little carpet but you need to check out the situation a bit before you committ. You have a couple of choices:
A) Bring your hand out of her pants and get a whiff of your finger to decide whether to go further
or
B) Procede in taking off the pants but leave on the panties. When the pants are off, kiss down to the stomach and slowly creep down with panties still on to see if everything seems OK to procede.
I haven't been with too many that I have had to turn and go the ther way with bt I know for a fact there have been a couple. And the strange thing, it wasn't the freaks...it was like it was the nice wholesome girls that didn't think they were going to give it up anyway so they didn't take care of themselves...