I read a lot in forums, about some sexual exploit, and the reply is-
'My wife/girlfriend would never let me do that.'
The obvious question here- 'How do you know?'
If your answer is- 'We discussed it recently, and she's just not excited by it.' There's the answer, you can stop reading now.
If your answer is - 'I JUST KNOW', or worse - 'I put my pinky in her bum on our honeymoon 36 years ago, and she said 'take it out', so she doesn't like anal'. Then there's a good chance she's talking to her girlfriends right now, and saying '.... put his finger in my bum years ago, and I wasn't in the mood, and he's never done it since, I sure wish he liked anal'.
Assuming your partner does not like something is just giving up without trying. At least ask.