1. ATC does make mistakes, and they might be wrong in shouting at you to reject the takeoff.
2. it is always up to the PIC whether he/she decides to follow instructions by the controllers.
3. ATC has used ''reject'' for very dumb things.
4. ATC has cleared me for takeoff with a fuel truck on the runway ahead of me. When I queried the clearance, they (atc) shouted at me that I should get the ear wax out of my ears and that I should takeoff...when I said...there is a fuel truck on the runway...they cancelled takeoff clearance.
so...be careful out there. I personally know a guy, then a copilot, cleared for takeoff in a DC9 at KORD...and there was a 727 crossing and stopping on the runway...he managed to takeoff considerably below V1 and kept everyone safe.
so...think NOW what you might do and remember you can fly considerably below V1/Vr...you might even want to know what VMU is for your plane/weight.
always know YOU have to know what is going on.