Consenting to one sexual act is not consenting to sex carte blanche.
This is true both morally and legally. The 2003 case of People v. John Z cemented into law that consent is an individual's right and may be withdrawn at any point during a sexual act. If you tell your partner to stop and they ignore you, it is legally rape.
Knowing you possess the legal high ground should assuage uncertainty, but sometimes we discount our own consent. To achieve adequate communication, we have to better articulate what we do and do not enjoy. Oftentimes, it's easier to have this discussion outside the bedroom, perhaps aided by establishing a safe word or phrase. And while this level of planning isn't always possible, that's no reason to stay silent.
Your pleasure and your comfort are just as important as your partner's. It doesn't matter if they made a long commute to see you or who paid for what. You are entitled to your bodily autonomy—it should never be overshadowed by someone else's preferences or fantasies. If you notice a negative emotion or thought mid-sex, examine it. It's tempting to wave away doubts or hold our tongues in hopes the sex will magically self-correct, but news flash: It won't.
Patterns become established and intensify, especially if assumptions are given room to flourish, so now is always the best time to speak up. And if that pattern has cropped up with a recurring partner, it's never too late to object.
Communication in sex is key, no matter how casual. Most of the time we make concessions in the hope of pleasing our partner, but sexual accommodation should never come at your own expense. Ideally, your partner would be tuned in to your nonverbal cues, but even with long-established partners, it's better to actively communicate. It's not unsexy to articulate boundaries—what's unsexy is feeling helpless or like an onlooker to your own sex life rather than a participant.
If your partner uses language you don't find appealing, especially in reference to you, tell them. It can be as easy as asking them to use another term or saying "no, thank you" to an invitation to a specific sex act. Hopefully saying this once is enough, but many times partners are so involved in their satisfaction that they need to be reminded. If you've repeated yourself to the point of frustration, let them know. Your boundaries override their wishes. If you don't feel like repeating yourself, you may want to consider getting separation.
Consent in consideration
A partner may suggest an unfamiliar, but not unwelcome, new sex act or kink. Honor your own indecision and give yourself time to consider the proposal. If the idea is exciting and you feel safe with this partner, explore something new while keeping in mind you can stop at any point.
If the idea is hotter in theory than in practice, consider talking through the scenario. This kind of theoretical dirty talk may end up turning you on, which can turn into mutual masturbation or solo play with you and your partner(s) in the same room. If you're not comfortable with the kink, try navigating the encounter back toward your comfort zone.
Of course, any sexual encounter can derail, which can present a complicated and stressful situation, so it's important to remember what's most precious. If getting out means leaving behind a sock or other personal item, that's fine. You're more than likely going to be able to get your belongings back, and even if not, what matters most is your safety and well-being. Catch a breath of air to gather yourself and examine if you want to completely end the encounter or not. Maybe you just need a moment, or maybe now's the time to call a ride.
Take stock of how you feel emotionally and physically (for instance, unusual dryness or penile softness). Sometimes as a defense mechanism, our mind distances us from stressful experiences in what's known as dissociation. Trauma compounds, so if you've experienced sexual trauma in the past, then you may feel especially triggered or numb.
Physical cues, especially from your genitals, can be objectively read even if you are mentally checked out. Treat these conditions not as a problem to solve but a symptom to listen to. Your body doesn't lie, so find a way to have a moment alone with yourself and ask your body if this is right for you or not.
Often we become so wrapped up in wanting to facilitate a satisfying experience for someone else that we discount our own experience. The pressures of the moment distract from our first duty, which is to ourselves. Your body has been with you longer than any sexual partner, and you'll still be living with it long after. Honor yourself, stand up for yourself and remember: The bedroom is the best place to be bossy.