Maybe the "Ugh" and the inflection that might have been taken from it which could be "if you don't feel like it" "then maybe another time?" is the issue?

I find it difficult sometimes to take inflection from written comments online; people may write how they speak but the enunciation and diction is not there. I get really shocked when someone thinks I've tried to offend them. I ask straight questions and try to give straight answers.

But communication is also the responsibility of the person receiving it; if they are in a no so good mood they are going to take what is said as negative or insulting or even rude. You can't be responsible for how he took the message unless you know that when you wrote the message to him that you were being "never mind whatever!" in atittude...Good luck with this