The girl/boy you went out on a date with, after you took her/him home, asks you if you want to come up 'for a coffee' but you are not interested. What is your excuse?

Of course most Jellies are very assertive and right to the point, and would answer something like “Look, I had a pretty nice evening with you, but I am sorry, I don’t think it would work out, the two of us.”
So, imagine you aren’t that assertive, more so, you are quite shy and not very direct.
What would be your lame, a bit cowardly maybe even, yet funny for the sake of the question excuse to not come for coffee?