Expression for two people whose similar personalities makes it difficult for them to get along?

I am aware of the concept of "personality clash", when two people can't get along because their natures are too different, but what is it called when two people can't get along because their personalities are too similar?

As Dan Bron says in a comment under the poster's question, one option is to use the expression "likes repel." Another option is to say that the their personalities leave the two people struggling with "contempt bred of familiarity."

Too much different or too much alike - it is still a 'personality clash'.

In practice, any ability to determine whether two people don't get along because they are too much alike, or too different from one another, is, to any professional working in the field, subjective. Relationships are far more complicated than that.

Ultimately it is something that skilled psychiatrists might not even agree about.

'Personality clash' has to be taken to refer to the product rather than to the constituent explanation. Otherwise we shall all need training in psychiatry simply in order to say whether there has been a clash or not.

The broken china is all the evidence I need for the existence of a 'personality clash'. Conversations in the street, about whether they are too much different or too much alike are entirely superficial.