From a cursory glance, it appears to be a rule up to free variation. Consider:
- From a naive search with the Google N-Gram viewer, it appears that
n' has a slight edge.
But if you zoom in to look at variations of
and eggs, as well as
ham and eggs, the picture gets murkier. Keep in mind that, since this is very informal usage, that it probably wasn't used frequently in the print media that the Google Ngram viewer searches through.
- Examples from popular culture:
- Variations of
Ham and Eggs, culled from search engines:
Conclusion: People tend to do one of 4 things to denote an unemphasized
As there is no broad consensus, and because people don't think about edge cases like these, I believe you could justifiably use any of them.