Even a tame bird can bite.  At any time.  A loud noise, a shadow swooping by the window, a vibration, can make your bird lash out at you.  Even if it's only trying to tell you, “Let’s get out of here!” When it's bird to bird interaction, they're both armed with the same, hard weapon.  But us?  Our lips are soft and sensitive.  A bird bites our tender lips and it's like a knife through butter.  I have heard some horror stories.  A double yellow head that nearly tore a woman’s lip off.  Or a totally tame cockatoo that wigged out and drove its beak through the bridge of a woman’s nose.  Serious emergency surgery followed up by a couple plastic surgery procedures was required. 

Can I put it any more clearly?  Kissing a bird on the beak is simply not safe.  And I'm not even going into the potential negative health affects your bacteria can have on your bird's health.  But that's something else to consider.

All you need to do is control your bird’s beak with gentle pressure while kissing it on the face.  Or nuzzling its neck.  Much more tender and sensitive than that rock hard beak. 

Also, if something startles your bird mid-smooch, you will be able to control its head so it can’t bite you.  With this technique I’m able to nuzzle and kiss birds that are not even tamed yet, as in the photo below.