If your dislike affects only yourself, then you might find a reason that is less fully truthful, but also less likely to dampen your friend’s enthusiasm on the day -- perhaps that, if you were officiating, you do not feel you would be able to enjoy her happiness as much as you would like.

My best friend has asked me to officiate her wedding to a guy I can’t stand. GENTLE READER: These are related, but separate, problems, which are going to require further inquiry into the reason for your dislike.

A reader is asked to officiate her friend’s wedding, but she doesn’t care for the groom; a married couple is at odds over whose parents get to stay in their house.