Grammar Warriors Mount Up

New grammar problem. A work sheet today read "My most favorite sport is ________" I immediately said "You can't say that because both are superlatives. You can't be the most tallest." The teacher answered, "Really, but that's what it says in the book." Gong, like Chuck Barris for not the first, nor the last time. I went back to the lab to huddle and research only to find that not every expert considers the word favorite to be a superlative. Some do. I would. But then again, I have no problem with saying "It is my least favorite." Is that because favorite is a positive so you can rank its negatives? I would stay away from saying "most favorite." You don't call John "The most dead Kennedy." We don't call Sartre "The most French." If we did either of these things, we would be making a joke. Thoughts?