That's easy to say. Believe it or not, most humans have limited strength, and if someone can't break glass it's not because they're not trying hard enough.

If you really want to break glass that's designed to be tough to break you need strategy not brute strength. Try tapping the top two corners of the glass and then the middle of the bottom of the glass, in an upside down triangle. You may be able to collapse the glass that way. Obviously you need a hammer/similar and a strong enough swing, and that is likely not enough for glass that's designed to withstand attempts at smashing. But the corners will be the weak points if you want to try.