You've managed to get yourself into a sticky situation. The perfect apology requires a delicate balance of guilt, regret, and manipulation. Here's how to do it like a pro:
Blame it on your pet. "Sorry, I was trying to feed my cat/ferret/parrot, and I didn't mean to spill the drinks on the carpet."
Or better yet, blame it on a natural disaster. "Sorry, the earthquake/tsunami/hurricane just made me forget about the whole 'clean up after yourself' thing."
Next: Step 3 - The Justified Lie Back: Step 1 - The Accidental Invitation Home