Brief Answer:
No major side effects, effectiveness reduced

Detailed Answer:
Hello, greetings!
Thanks for posting your query in hcm.
Usually use of expired KY jelly will not have any untoward side effects. However, the effectiveness of KY jelly will be reduced.
If you have used KY jelly vaginally, just douche the area with warm water.
If you have any discharge, itching or discomfort, then it might point towards a yeast infection for which you might have to apply antifungal medication.

Thus, for now flush with warm water and observe for any signs of discomfort.
If you have any further doubts/ clarifications, please feel free to ask.
Regards,
Dr. Sonia

---