How about dinner with a group of friends?
Sure. That's easy. First, know everything. It doesn't matter if the conversation is about the weather or sports or politics or leafy greens or quantum physics. Know it all. You'll obviously have to fake it, but that's fine. However, you can't expect to ruin dinner with a group of friends if you don't share your "knowledge". And remember, delivery is key.
You must speak loudly. Your voice should be so loud that it over drives your friends ears, making them completely useless other than to hold up a pair of glasses. You want people to receive your words by absorbing them as they penetrate through the skull directly into their brains. Deaf people should complain about the vibrations on their bodies. Babies should cry when you talk. Dogs should howl. Cats should (and will) look annoyed. Pretend you need to be heard from across the room with a pillow over your mouth while music is pumping and a construction crew is jack hammering and making all kinds of unnecessary ruckus like they always do. Yes, people will want you to shut up. That's perfect. But they won't tell you to shut up. Instead, they'll sit there and politely pretend that your intense volume level isn't bothering them and that you are interesting.
Then you must touch someone. Well "touch" is not the right word . Replace it with "grab and shake". Pick a victim and place your hand on their shoulder. Begin to shake them and compress their shoulder until they become short of breath and nearly pass out. They will begin a process of vigorous head-knodding as if they vehemently agree with whatever you might be saying. But they don't. In fact, it kind of sounds like complete bullshit. Everything you say needs to seem like complete bullshit. That shouldn't be difficult since you are faking your knowledge anyway. It needs to be so loud and annoying that, if the government got ahold of it they would build a massive speaker array on the west coast of Alaska and aim it a Russia to drive them out of Asia. And don't forget, you need to squeeze that shoulder good.
With the knowing of all, the loud talking, the grabbing and shaking, and the bullshit, you are most likely to have ruined the evening for everyone. If it still looks like someone is having a good time, continue the process until everyone is ready to leave. Be careful! If they bolt you might get stuck with the tab. Excuse yourself to the restroom, ask the server for the checks on the way, and just leave without another word.
Your Friend's Son's first birthday party?
It's at 1:00. Ignore the time. Do not leave for the party until your friend calls or texts you asking where you are. That should allow you to show up between 1:33 and 1:42. Plenty late so that everyone thinks you forgot. They won't be expecting you to have a gift for the little slobber box.
Back up a bit. This takes some preparation. Before you leave, throw about twelve of those 16-ounce cans of Stag in a cooler and ice it down. You're going to wheel that puppy into Chucky Cheese's. Sure, you'll get some looks. You might even get scolded by some overzealous teenaged employee. See the techniques in the dinner party example above. A little taste of that and they will leave you alone. Teenagers don't have the stomach for it.
Since you were late, you hopefully missed the overpriced cardboard pizza. Ask for some anyway. Then grab some cake. Eat it fast and make a mess. Pretend you are one year old. The birthday boy should have to compete with you to see who can be the most covered in icing. Throw back a few cans of Stag while you're at it.
When it comes time to open presents, sit patiently and wait for an opportunity. You'll need to snatch away a good-sized chunk of used wrapping paper. This will be harder than it sounds. Everyone knows that a one year old loves the wrapping paper more than the present inside, so he may fight you for it. If you are good at this, you'll make him cry.
Once you have the piece of used wrapping paper pryed away from the bawling child, grab a can of Stag from the cooler and wrap it up with the paper. Hand it to the cry baby. Maybe he will stop crying, maybe he won't. Doesn't matter. At this point you are more than likely going to get dirty looks from several adults. Someone will probably say something like "What are you doing?". To which you will reply, "Giving an awesome gift, that's what! It's baby's first beer!"
When the kid's parents grab the Stag and bitch at you, you should respond; "See! I knew his parents would be too pussy to get him a gift like this!" Grab a Stag, chug it, smash the can in the rest of the cake, take your cooler and leave. Shout obscenities on the way out. Make sure the birthday kid is crying as you do. That should ruin it real good.
How about A funeral?
For this one you'll need a few things if you want to ruin it right.
1 Large bottle of Bourbon
1 Canary Yellow golf shirt
1 pair plaid shorts
2 white tube socks
1 pair sandals
1 pack of Parlament cigarettes
7-10 tasteless death jokes
Take one shot of the bourbon. Put on the golf shirt, the shorts, the socks, and the sandals, taking a shot of bourbon in between each item. Spill a decent amount of bourbon near the collar of the shirt. Smoke 2-3 Parlaments at once and roll the pack up in one of the shirt sleeves. Rehearse the jokes in the mirror. One more shot and you're ready to go. Take the rest of the bourbon with you.
If you've followed the instructions precisely, you don't have to worry too much about anything else. You are bound to ruin this funeral. When people see your get-up, they'll feel the disrespect. Every crying relative you hug will smell the bourbon and the cigs. They'll probably wish they could have some. It's ok to share. Get the immediate family of the deceased together in a circle and pass the bottle around. When the second round is done, offer up the smokes. One more round with the bottle and you can start telling the jokes. If the bourbon is working, they'll be laughing. A few will be stumbling, one kid will puke on gramma. If anyone needs to urinate they can use the open hole in the ground. The rest of the funeral-goers will be watching with disgust. The master of ceremonies will ask you all to leave. Convince the family to tell him they want the body back. Help them load it in Uncle Randy's van.
You're job is done.
The scenarios presented above are just examples, but I'm sure you can use the techniques demonstrated here and apply them to other situations. Make them your own. Add lib if you like. Try it in a business meeting or at a movie. Practice practice practice. Pretty soon you'll be able to ruin almost anything.