He probably was just trying to impress a date, but that's enough of a problem. Everybody involved with anything deadly, especially self-replicating deadly, should be serious people.

He started off good by saying he was lying and that's all he had to do, just continue diffusing their questions by taking responsibility for being irresponsible on the date. He'd still get fired - which he should be - but could get a job somewhere else because he would have a believable story that he made a mistake and owned up to it.