What is the difference between “Honte à toi” and “Honte sur toi”. They translate the same:
“Shame on you!” I couldn’t find any explanation. Are they synonymous or is there a difference?
According to the dictionary, they mean the same thing.
Yup. I think it’s just a matter of style - similar to the English phrases “bring shame on oneself” and “bring shame upon oneself”. It’s hard to think of a context in which you could use one construction but not the other.
Thanks, so ‘à’ and ‘sur’ can be used interchangeably. If anyone can point out a rule that states this option I would really appreciate it.
I have not seen any formal rule, not that I searched through every conceivable reference grammar, but you can easily look up attributed quotations, see for example
https://www.cnrtl.fr/definition/honte
as well as search through corpora yourself.
Thanks DPRK.
Since I don’t speak French, how are they pronounced? Is the first one ‘Honta twah’?
Close, except that the ‘H’ is silent.
‘Onta twah’. Mercie.
Merci is spelled without an “e” at the end.
Mercy bucket to you too, RayMan!
I don’t speak French. 
They can be used interchangeably in this context, but obviously there are many other contexts in which this is not so.
I suspect the choice of preposition may depend on which verb is being used. Google offers numerous examples of variations on both “apporter honte à” and “apporter honte sur” (both meaning “to bring shame on/upon”), so presumably both are acceptable. But “faire honte à” (to disgrace) seems to be used while “faire honte sur” is not, and presumably a French speaker would understand “faire honte sur”, but would regard it as not idiomatic.
Thank you USD1. That clarifies things much more now.