Validate Data in The excel through Macros coding Based on two columns of data.

I have my data like this :

ColA    ColB

Ram    milk

Hem    milk

Ram    bread

Hem    Noodles

here i need to check whether If Ram has milk in ColB he must have Bread in ColB else error message should be populated.Here in the sample data given above it should generate a error message saying that HEm does not have the bread in colB .

This check should happen if i click on a button in the sheet through macros coding.Please help .

Thanks in Advance,

Janaki S