Morris, the old professor, visits his doctor for a routine check-up and everything seems fine. The doctor asks him about his sex life.
"Well..." the professor drawled, "not bad at all, to be honest. The wife isn't all that interested anymore, so I just cruise around. In the past week I was able to pick-up and bed at least three girls, none of whom were over thirty years old."
"My goodness Morris, and at your age too," the doctor said. "I hope you at least took some precautions."
"Yep. I may be old, but I'm not senile yet, doc. I gave 'em all a phony name."