Snap or Chill?!

Okay so... I went to the movies with this guy from work. The date went horribly & afterward I told him I wasn't trying to kick it with him anymore because he got immediately clingy like he was my boyfriend or something. Since we work together, he always had an odd look on his face when he sees me talking to coworkers of the opposite sex. This guy pulled a female friend of mine into a private conversation & basically interrogated her! I want to snap on him, but I have to keep in mind that this is a work environment. Granted, it was a huge mistake to get involved with someone from the office, but ONE DATE (no sex or kissing, NOTHING) & he's all Michael Ealy from the Perfect Guy. WHAT SHOULD I DO?!