The social bond categories are 0 = strangers, 1 = acquaintances, 2 = friends, and 3 = kin and life partners, more details here. Perhaps this would be a good litmus test for how close you are with someone?
Note that merely reading about yawning is often sufficient to elicit a yawn.
Reference
Norscia I, Palagi E (2011) Yawn Contagion and Empathy in Homo sapiens. PLoS ONE 6(12): e28472. doi:10.1371/journal.pone.0028472
