AIBU to think this is very rude

I always read them. It just seems natural. I probably wouldn't do it in friends' houses, or not without asking first.

We always read family cards too, I don't think it is rude, if they are on display.

I always write very little in DH's cards precisely because I know that people will automatically be picking them up and reading them.

If you put them on display people assume they can read them.

We all do it in our family, not that there`s ever anything outrageous in ours, not so far, anyway.

I presume that they are either the brother or sister of your DH? I'd read my siblings' cards if they were displayed. I was "dying" to read the wedding anniversary cards my son and his wife had exchanged so I had a peek when they were out and I was babysitting.

I would almost go so far as to say it's hard to resist reading cards that are on display.

Some people think it is rude. Some not.
Some do it almost automatically.

Oh I do that as well . But probably only with family. I always look at the birthday cards at my daughters house. Then again, I wouldn't do it till they'd gone out [I usually babysit for them on her birthday].If it was my DIL's birthday I wouldn't look at her cards.

Honestly NanKate I don't expect they thought it was rude, for the same reason as everyone above ie. they were on display.

A lot of people do that. If the cards are on display I expect they thought it was OK to have a look...

Birthday cards are not private if they are put out on display so I don't suppose they thought anyone would mind.

My DDs always look through the cards that we display - I think the principle is not to display any that you do not want to read by anyone else.