"Anyone is allowed to leave an uncomfortable situation at any time. Each person’s feelings of comfort and safety are more important than participating in the game. If a problematic situation comes up and someone doesn’t feel like continuing the game, it’s all right if they step out. It doesn’t matter the circumstances of how it’s in the game—perhaps someone made a joke comment, or an aspect of this issue slipped into the scenario accidentally, or it’s being introduced despite that person not consenting to it. The person who is feeling uncomfortable doesn’t have to confront the group about it (especially if that would make them feel more uncomfortable), they can just leave the table. … If they don’t feel comfortable with talking to anyone about it or don’t think the situation will change, it’s fine to not play in that game for a while, or permanently." —Consent in Gaming, pages 4–5
For some reason, there are people who think that the Consent PDF is arguing that one person with a fear of spiders gets to cancel an entire campaign about fighting drow. If the GM has plans to run a spidery drow campaign, and four of the five players are all-in for that, and the arachnophobe player doesn't want to play that, there's nothing wrong with the arachnophobe not attending those games. There will always be more games to play in the future.
In other words, saying, "I think this adventure/next few sessions/campaign we're planning is probably something you/I should skip" is perfectly acceptable. Just like it's okay if one player decides they want to skip board game night for a while because the group wants to play Pandemic instead of Catan. Just like it's okay if one person decides to skip movie night because they don't like rom-coms and the group is having a Valentine's Day rom-com marathon. Or for your vegetarian friend to skip going out to eat after the game this week because everyone else wants to try the new barbecue place. Or whatever.
The Consent PDF is a safety tool to help you identify and prevent potential issues before they pop up in the game and cause someone trauma.
Sometimes you prevent that issue by saying "no romantic or sexual content in the game"
Sometimes you prevent it by saying "we can have flirting and romance, but we fade to black for any physical intimacy or sex."
And sometimes you prevent it by saying, "the next couple of sessions have a lot to do with a particular brothel and how the nearby town's misogynist mayor is claiming ownership of the unborn child of his favorite prostitute at the brothel*; Chris, I know sexual stuff in the game bothers you, so maybe your character should go elsewhere for a couple of weeks and we'll have you rejoin us when we're done with this part of the storyline."
* Hey, it's a Firefly reference!
Likewise, sometimes you prevent trauma by saying "no spiders in the game."
Sometimes you prevent it by saying "spiders in the game are okay, but let's not have creepy descriptions of their chittering mandibles, dead eyes, and bristling hairs." (Which, mind you, is literally one of the example situations in the Consent PDF.)
And sometimes you prevent it by saying "I bought this really cool drow-focused adventure that I'm really excited about running, it'll take us a few sessions to get through it; Chris, I know you don't like spiders, maybe you could take a break from the campaign so you don't have to deal with this in the game? Maybe I could run you through a short solo campaign on the side."
It's about accommodating the needs of the people at your table. And sometimes the best way to do that is for someone to skip a session or two.