Your friend is right.
I have this girl who knows me from my AFC days. Before when she asked me where I was going, I would answer like ''Me and my friends are going to play videogames'' or ''I'm just going to hang with my friends''.
Lately we started talking again and when she asks me what I'm doing on a friday night I just answer like your friend said ''I got a thing I need to do''
She also starts to ask me if I've made out with anyone or kissed anyone. She have only asked this twice but the first time I just replied ''Who have you been talking to?'' and changed the subject. The second time I made it sound like I was lying ''uuh, no.'' and changed the subject
Hope this helps
Also did a quick google search for you and found:
1-vt88223.html?start=0 and
http://www.mademan.com/mm/how-be-more-mysterious.html