You look lethal today

I just don't understand my colleagues. Ask one simple question, and they misunderstand and jump all over you. They search for hidden meanings in E V E R Y T H I N G that one says. I have lots of examples and here's one:

Daftie: 'You look lethal today.'
MrT: 'I have no idea what you you're talking about.' - I was clueless
Daftie [annoyed tone]: 'FUCK OFF, MrT! DON'T TAKE THE PISS OUT OF ME!' [and she stormed out of the teachers' room].

Puzzled by this bizzare run-in, I asked Talkie (who also in the teachers' room when it happened) if she knew what Daftie had meant, and she didn't either.