Where to draw the line?

Maths is so perfect and precise. It deals with - well at A level maths, anyway - it deals with 'neat' stuff. (It gets not so neat, after a while. Apparently not all triangles are 180 degrees and degrees according to my maths teacher is not a proper number, so that is why radian measure is used.)

I cannot help but noticing that life is so different from maths. In maths there a lines; however in real life, there are a lack of distinct lines.

What brings this on is that today I was in the library with my friends and Haya had some unused cue cards and asked if we wants some then she insisted we take them because even when she got to Uni, she would not be able to sue them all up. Now another friend of mine, who will remain nameless said to here, was like well you are not even going to get into a uni. She never said it a joke way. She said it in a matter of fact way. Aisha and me just stared at here, like, what the flip is your problem, whilst Haya, who the joke was directed to, laughed, as if it were a joke, though it was obvious she did not take it as one because she said, I know I won't get into a uni.

I was thinking about it on my way home. Like, definitely, a line was crossed. However,. if the person were to just think it without saying it out loud, would that cross lines too? I mean, is it okay to think mean stuff, but just not say it? or do things only become mean when another person hears it?

So I was thinking, she crossed a line and should have definitely kept it to herself. Then I thought, well hang on, I am a person who tells people to say what is on their mind. Granted what she said was mean, but if I told her, yeah, by the way, tell me what is on your mind, the judge her for doing so, what sort of person would that make me? A hypocrite yes, but would I, being the person giving you a false sense of freedom to say what you want,  be worst than there person who says something mean?

How do you draw the line between things like this? I do not think you can. Is there a difference between thinking something mean and saying it, or does saying it and acknowledging it out loud make all the difference?