1. Look at them in the picture. Both have, well, very similar design and pose. Both have close gap between the eyes, wide mouth, and long nose.
2. Both appear in the middle of the story and become the new guide to the 'adventurers' which are Joy as Anna and Sadness as Kristoff (the former guide as well as the map).
3. Both are easygoing, cheery and talkative, also, of course, imaginative.
4. Both have something to do with the past memories. Moreover, Olaf was an imaginary friend of Elsa and Anna. While Bing Bong is Riley's.
5. Cannot read. Although unlike Olaf who cannot neither read nor spell. Bing Bong can spell D-A-N-G-E-R.
6. Both say, 'I can't feel my legs.'
7. Both should have died in the end. However, Bing Bong is for real while Olaf is 'rescued' by Elsa.

Well, so far those are the ones I can think about right now...

i agree with you completely! And Riley has forgotten him, just like Elsa while Joy immediately bonded with him back, just like Anna.

I didn't notice this at first but now that you mention it...

^Same here.

Well, from the very first time I saw Bing Bong appear in the movie, my instinct had told me that he is very similar to another character, which is Olaf!

i never noticed it until u said it wow!

They have the same kind of role in their respective movies anyway, but nice work pointing out all those little similarities they have too! ^^

They should be friends.

I'd say so. But I prefer Bing Bong :'( <3