A lack of filter means saying whatever is on your mind without considering politeness, appropriateness, relevance, or respect for the situation. People who have no filter may use profanity when they should not or bring up sensitive topics such as religion, politics, sex, body parts, or body odors in ways that offend others. Human communication follows social norms, and these norms discourage creating unnecessary controversy, embarrassing people, or discussing highly divisive topics in casual conversation. When someone ignores these norms, they may be seen as awkward, weird, or socially unaware, and others may feel unsafe or uncomfortable interacting with them. Appropriateness is a skill that can be learned by thinking before speaking, considering the audience and situation, and asking whether something is respectful, relevant, and suitable to say.
I wouldn’t want the listener to be uncomfortable or worse inadvertently hurt while delivering the message in the best way possible. Being appropriate is certainly the key but the listener too has a key role to play in taking the message in correct way, for this trust and intent needs to be established first as it is possible for listener to interpret the message in a construed or improper way, or worse make a normal thing sound bad or weird.