Buffy the Vampire Slayer's Nicholas Brendon apologized Monday for his "unacceptable behavior" in Boise, Idaho, which resulted in his arrest Friday evening. The actor, 43, posted the apology on his Facebook account Monday morning and said he acted out after mixing prescription medication with alcohol and is intending to seek treatment for his "medical ailments" and "emotional demons." "For the past 5 days, I have been taking prescription pain medication to help me manage a cyst behind my knee cap, which is scheduled for corrective surgery on Monday morning," he continued.