The holidays are supposed to merry and jolly and all that and a pack of crackers, okay? So just do the universe a solid and don't be a jerk this season. It's really not that difficult.
My guess is that you love your friends and family, yeah? So why hurt their feelings? The last thing you'd want to do is add extra salt to Thanksgiving dinner or poison the Christmas cookies with a feud. So here are some things you should keep in mind if you want to preserve the holiday cheer.
1. Remember that you are not entitled to make rude comments just because you're a relative. Literally the most common thing during the holiday seasons is being insulted by a relative because they think they have some sort of "pass". Well guess what, honey - that's not how it works. If you insult someone, it doesn't matter if that person is related to you or not. It's rude and unnecessary, and you're a big ol' jerk for making a jab in the first place. Just go the safe route; smile, give a firm handshake or a warm hug, and tell them you're glad to see them.
2. Don't make a huge deal out of the presents (or the money spent on them). No one wants to be around the person who makes a big deal out of the gifts. If you're the adult version of Dudley Dursley, you'll be spending the holidays alone because no sane person would want to deal with your greed. People have their own financial situations - so no matter if it's a handmade card or a golden goose egg, just smile, say thank you, and move on.
3. Respect guests, hosts, and property. Basic manners, people. Come on. If you're a guest, thank the host for the invitation, use proper table and social etiquette, and for the love of god, don't break anything. If you're the host, introduce people who might not know each other and be sure to accommodate for food allergies and children. (NOTE: Whether you're a guest or a host, it's probably best not to get extremely drunk. But I mean, hey, if that's your thing, go for it. Have a jolly turn up.)
4. Avoid controversial topics. Everyone's got that racist grandparent or extremely outspoken uncle, but don't let them start a conversational wildfire that takes over the whole shindig. It gets awkward, loud, and angry, and it makes for an extremely uncomfortable gathering. WE all have different opinions, okay? So if you value the relationships with your family or your own sanity, you'll keep your mouth shut about the election, abortion, immigration, or any other extremely inappropriate subtopics. (WARNING: If you ignore this nugget of wisdom and decide to strike up a conversation about the election that results in you getting punched in the face, just know that you were warned.)