If this is a traditional biology lab, this is a violation of so many lab protocols it's not even funny. Possible contamination of samples, the rattling could knock over glassware, NOT TO MENTION not wearing correct protective attire in an environment that frequently handles dangerous chemicals!
If you're going to have sex in the lab, you have to use protection for not just your genitals but also the rest of your body, ensure you have a clear space to do so, ideally lay down something disposable on the floor to pick up any potential stray contaminants, and of course clean up THOROUGHLY afterward. And yes, the lab coat would have to stay on.