Well...really it should be Siobhán (note the accent on the "á" making it a long vowel sound)
All my children have Gaelic names and they get just trashed everywhere they go. If we're ever at the doc's and they call out any one of the names, if there's a long pause before the pronunciation attempt, we just stand and say that us!
My Siobhan gets called "Sio-bow-han" and "Sheffan" quite a bit. Surprisingly her nickname at school is Nahbois (Siobhan backwards) which she made up on her own. Then my Aoife gets "Oi-Fee", "Ava" and "Eva" all the time and Roisin gets called "Raisin" or "Roy-sin" quite a bit too. We should have moved to Ireland and there would have been no issues.