* IHY: I hate you (though it's often used playfully and sarcastically, especially between friends)
* IHU: I hate you (same usage as IHY)
It's important to note that these abbreviations are often used ironically or playfully, especially among friends. The actual meaning depends heavily on the context and relationship between the people involved.
If you're unsure about the intended meaning, it's always best to ask for clarification.