depends entirely on the context

When hugging anyone in public, squeezing the ass is generally inappropriate. In private, keep it to someone you are actually going to bed with or have a realistic chance of going to bed with soon. In other words, not young girls. I'm sure there are some exceptions, but that seems to be the general rule in America.

Now, the diagonal-arm-hug is another matter. This hug can either be done side-to-side or face-to-face, er, face-to-chest.

The hugger drapes his arms around the huggee but does not raise them.

Her's a side-by-side extended-arm hug. This looks best in a monospaced font like courier.

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If this is looking from the back, note the right-arm of the man is extending to the right-arm of the girl. If the girl were a woman, they could be holding each other's right hand. Since the girl is a girl, the man's right hand will probably rest on the girl's right elbow or a bit below that point.