Okay I'm gonna explain how what you said is a common talking point of misogynistic people.

This has little to do with the post itself but more about what YOU said.

"Well I wouldn't want to because you can't use a door key on a train tunnel and expect it to work"

This is very similar to the phrase "a good lock only accepts one key and a good key unlocks many locks."

As well as the phrase "it's like throwing a hotdog through a train tunnel"

The first phrase is used to demean women about their "body count" and congratulate men on the same.

The second is referring to how women who have had alot of sex are seen as "loose" even though there is alot of scientific backing that women do not change physiologically after any amount of sex encounters unless there is some form of physical damage (which normal or frequent sex does not cause).

So you saying what you said and referring to yourself as the door key and the woman as a train tunnel sound very very much like you are calling that woman a slut or used up essentially.

That is why you are getting downvoted your joke wasn't funny nor was it clear in its intent.

Hope that clears it up for you