Common Accidental Innuendos
- Comments relating to size: Since there's cultural ideas about both the size of breasts and penises (see Buxom Is Better, Bigger Is Better in Bed, Teeny Weenie, A-Cup Angst, Gag Penis, and D-Cup Distress), some people will take any size-related comment (for example "it's small", "it's huge", "they're too small", etc) as a dirty joke. However, size is an important thing sometimes, and people do get impressed by things which are unusually big or small, so sometimes this is hard to avoid.
- Objects that look remotely like body parts: Some people think that pretty much anything longer than it is thick looks phallic, especially if it has a rounded tip and/or anything on the end that could remotely look like balls. Two round things next to each other might also be taken as looking like breasts, a butt, or balls. However, many things are round or longer than they are thick, so it's rather common to get an unintentional version of the trope Something Else Also Rises.
- Words with double meanings: Some words ("gay", "queer", "faggot", "ejaculate", "molest") initially had an innocuous meaning but developed a naughty meaning that became a lot more common. Others ("arouse", "wet", "hard", "wiener", "erect") have an innocuous meaning that's as common as the naughty meaning but too easy to make sound dirty. Then, there's also names ("Dick", "Willy", "Fanny", "Wang", "Johnson") that have double meanings. In some cases (such as "Wang" mentioned above") this is due to the name being from a different language. Sometimes, the naughty meaning of a word is more or less common in different places (for example, in some places "fag" is nearly always short for "faggot", but in other places, it's slang for "cigarette").
- Words that only sound like something naughty: Often used for intentional innuendo, but is also often accidental. Famous examples are "masticate" (a relatively unusual word for "chew" that is famous for sounding like "masturbate") and "Uranus". Sometimes, this trouble arises from words that simply rhyme or alliterate with naughty words. It's also common with nonsense words, especially if they are verbs that come before a pronoun/name or nouns that come after a pronoun/name (for example, if Alice says, "Bob zeeped my blorp", people might see that as dirty, even if the writers only meant it to mean "Bob took my last cookie").
- Phrases that sound like sex acts: Common are the number 69, and talk about "getting off", "being inside someone" or "pulling out".
- Someone who just happens to awkwardly look like they're doing something sexual: Holding a hand or an object too near one's junk can result in what is basically an out-of-universe version of Mistaken for Masturbating. However, this is usually not taken as dirty if there's a clear reason for it (for example, they're doing the Potty Dance or covering themselves up due to being naked). It's also common for a Suggestive Collision to only come off as suggestive unintentionally. Moaning, heavy breathing, and certain facial expressions can often come off as looking like an orgasm too, which seems to be more common if it's a woman.
- Any of the above if something else awkward is happening: Generally, people are more likely to have their minds in the gutter if the person onscreen/on-page/whatever is talking to or about someone they're attracted to or who's attracted to them or who the audience ships them with or who is genuinely a bit lustful, or is naked or near a naked person or a combination.