At the risk of stating the obvious whilst using a cliché, funerals are generally depressing affairs (unless they're Scottish funerals in which case funerals are generally excuses for getting drunk and having sex on accordions). Because funerals are often depressing, you may want to try to liven them up with your wit and antics. Don't do this.
It's not that you're not witty or that your antics aren't funny. I'm sure the years you spent watching DVDs of Louis CK have prepared you for a life of injecting humor into any and all situations, regardless of how many accordions may or may not be present. I get that, but it's not you, see, it's all the people crying over the dead person (or "deceased" if you want to sound like a person who has ownership interest in a hearse).
Remember to honor the dead by remembering them lovingly, even if you're glad that said dead person is on his or her way to hell. As someone who has misbehaved at funerals in the past, I have learned the hard way what is and is not acceptable behavior at a funeral. The following advice should be heeded at all times in all non-Scottish funeral/visitation/wake/internment situations.
There is only one right way to comment on the appearance of the deceased… if the funeral is open casket, that is. There is no right way to comment on the appearance of the deceased if you cannot see the deceased. You would think this would go without saying but people are stupid and may say things like, "Wow, you're grandpa really looks like a casket."
Anyway, assuming the funeral is open casket, you may only say positive things about the good job the dead-person-makeup-artist did on the corpse (also, you can't say "corpse"). You cannot call the deceased sexy or ugly or fat or thin or just generally kind of frumpy looking. All you are allowed to say is, "Wow, he/she looks great. They really did a heck of a job." You can comment positively on the clothes the deceased is wearing as well, but don't overdo it. I mean, no one wants to go to a funeral with the person who comments on the fashion sense of a dead body.
Now that you understand what you can say about the body, it's time to learn what you can say about the person who once occupied said body.
There is only one way to remember a dead person: lovingly. You can't have it any other way. In fact, here is an exchange that occurred between two friends of mine a few months ago (all names have been changed to protect me personally because I have enough problems):
Kip: She used to date that guy who tried to rip us off a couple of times. What was his name?
Bill: James.
Kip: Man, I hated that piece of shit.
Bill: You know he died in a motorcycle accident last year.
Kip: Really, he's dead? Well then I wish I had gotten to know him better. I'll bet he was a great guy all in all.
You see, there is a reason dead people have funerals and that is so they can be held in loving memory. So there's your only way to remember any dead person at any funeral: lovingly. You can't remember them for being mean, drunk, rude, boisterous, or anything other than that which you loved and which brought light to your life. At funerals, you must remember to honor the dead by remembering them lovingly, even if you're glad that said dead person is on his or her way to hell. Also, you can't bring up hell.
At funerals, all dead people are going to heaven. No one wants to think for one second that their loved one doesn't deserve a totally cool afterlife with all the bells and whistles salvation provides. So never say anything even casually touching on the slight possibility that you will see the deceased in hell. We all know what you did and we all know where you're going but there's no reason to bring that up in polite funeral conversation.
Other funeral-behavior pro tips:
Do not bring your own food or drink to the funeral. Snacking on gummy worms and guzzling airplane bottles of bourbon may seem like a decent way to pass time at a funeral but really it's just rude both to those who would like some candy and liquor, and to those who would like you to spend the funeral lovingly remembering the person who became a corpse. This is not high school, it's a funeral, and sneaking in liquor and candy simply will not stand. Jerk.
Unless asked to do so by the family of the deceased, do not sing. Now, I'm not saying you don't have a great voice but there is a time and a place for everything. Also, your voice sucks.
Keep your clothes on. Seriously, I shouldn't even have to type that.
Funerals are tricky events. You simply don't get to be yourself at a funeral, which is why I recommend behaving like Mr. Rogers or Roy Rogers. Those guys were always classy. As long as you keep your clothes on, keep from singing or shouting, don't bring your own food or drink, remember the deceased lovingly, and don't comment negatively on anything related to the deceased, you should be okay at any funeral. Unless you're the guy who brutally murdered the dead person, in which case you should probably just stay at home and clean your gutters or something.