'I' before 'e' except after 'c' or sounding like 'a' in neighbor and weigh. There are some exceptions to this that you just have to know such as sheik and accuracies; but when in doubt, follow the rule.
I usually go a different route and say how I've been really ill, but that I'll fill out again soon. Usually gets a more satisfying response. (Yes, I'm really mean, too.)