Here are a few examples from some of my favourite photographers:
Jeff Wall's "Mimic"

Tina Barney's "Jill and Polly in the bathroom"

Nic Nicosia's "Like photojournalism"

Recently though, my sister tuned me into a hilarious new website devoted to (unintentionally) awkward family photos that give new meaning to the word uncomfortable. Simply put, you can't make this shit up.
A few selections from the website.
"Family tree - even the tree thought this one was awkward"

"My two dads - feel free to use your calculators for this exercise"

"The closeness of you - when you're madly in love..."

There's one image on the site for which there simply are no words. Even I hesitated to post this one - "The Wonder Years" . Yikes.