Jess and Dave Osinski like to share their vacation photos on Facebook. In 2013, the Wauwatosa, Wis., couple travelled to Peru, New York, Florida and San Francisco.

This month, they got an anonymous letter in the mail adorned with a yellow smiley sticker, the Journal Sentinel's Jim Stingl writes.

"It's a little upsetting seeing, hearing and reading about someone's vacations all year while we all can't afford one," the letter read. "Go have some kids and don't be so selfish as to only think of yourselves all the time."

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The couple – she's 36 and he's 41 – have made the choice not to breed. Now it's clear someone in their social circle isn't into their seemingly unencumbered lifestyle.

"That's an editorial I don't need or deserve," the husband told the Journal Sentinel. "How do you know what we do? We do things. We're Big Brothers Big Sisters to somebody. We give back in our way. We chose not to have children. It's just our decision."

His point underscores incendiary research that has found childless people volunteer and pitch in more frequently with family and neighbours than their married counterparts, and that's despite charges of "being selfish" from out-of-touch relatives.

The mystery letter writer asked that the couple please send ordinary Christmas cards, and not collages of their fancy child-free getaways. (This means the sender is likely a family member or close friend.)

Given that the writer was privy to her Facebook pics, the wife decided to post the letter to her Facebook wall with this note: "Please feel free to unfriend us from Facebook as we clearly are not 'friends.'"

Commenting on the story, Mommyish blogger Maria Guido wrote, "Some people use [Facebook] to seethe with jealousy and anger about their life choices."

If a Facebook friend's abundance of leisure time sends you into a blinding rage, why not just block them, Guido suggests.

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Sure, that or hide their notifications from your newsfeed and seek professional help.

"I'm beginning to think parenting really is the 'hardest job there is,'" wrote a reader on the Mommyish story. "It must take a LOT of time to write sanctimonious letters to everyone you know who's daring to enjoy their lives before or without kids." And another: "Presumably, no one forced you to have kids, so why the martyrdom?"

But the most measured reaction came from a parent: "I have kids and I do plenty of travelling and fun. These people are just being crazy."