Notes

"I have the squirts/diarrhea/stomach bug" is never, ever questioned. Ever. If youre going to skip a class, the "Dead relative"/"family emergency" thing is not good, unless you bring it up a few weeks in advance, like before a class a couple weeks before you're going to miss, tell the teacher "hey, I just wanted to let you know that something came up with my family, so if my cell phone rings during class, and it's my mom, I will have to excuse myself to take the call". When the phone doesn't ring, the teacher still has the seed planted that there are problems, even if you never have to excuse yourself. Even better if you get a friend to call you mid-class, so you "excuse" yourself to take it.

the "family crisis" takes much planning and fore-thought. You can't just tell your professor 2 days before you miss a class that "something came up". At that point, it's better to not say a thing, skip the class, and then about 1/2 an hour before the class, shoot them an email with "I thought I'd be able to make it, but I was up all night with a nasty stomach bug that I think I got from my roommate...please let me know how I can make up for the class I will have to miss, since I don't want to get anyone else sick".