Nick Reiner pleaded not guilty in Los Angeles on Monday in the killing of his parents, Rob Reiner and Michele Singer Reiner.Nick Reiner, 32, was charged with two counts of murder in the first degree in the fatal stabbings at the couple's home in LA's Brentwood neighborhood in December. His public defender, Kimberly Greene, entered the not guilty plea on her client's behalf.Reiner sat in court behind his attorney in a glass-enclosed custody area. His head was shaved and he wore brown jail clothes.Reiner spoke briefly during the arraignment, saying "yes" when Los Angeles Superior Court Judge Theresa McGonigle asked him to acknowledge waiving a speedy preliminary hearing in his case, as requested by his attorney.…