is it masclinine or feminine or both to respond to " what's up" with "nm, bored, you?"

It's proud...basically says "Usually I've got something better to do...but now I'm left with this you should be lucky to have me around". Kinda like saying "that's nothing, I've seen done/done/had...that a million times; it is posed by people as a cheesy way of saying "I'm experienced."

I suppose you could say it's masculine because, say if one person says "I'm bored" and the other says "this is great", the person who says "I'm bored" is often viewed as the "alpha/superior" male...the feminine way of doing that would be more like wearing a shirt stating "I'm dating your boyfriend".

And, I agreed with a previous answerer, teenagers take that "bored because I'm so experienced" attitude plenty.

Neither. It's teenagerish.