I had a moment just like yours when I was about 21 at university. Was with a group of close friends and blocked really badly for about 5 solid seconds. I was so embarrassed and I went into a bit of a depressive episode for a few days afterwards, since it hadn't been that bad in a long time. You do learn to just roll with it, or at least I have. I try and make a bit of a laugh out of it now, but I realise this approach is not for everyone.