Reference conversation, said warmly, with a small laugh: "彼はマイペースだから。"
Read one way: he's relaxed, he does his own thing, lovely energy.
Read the other way: he ignores deadlines and does not read the room, and I am not going to say that out loud.
The laugh is where the information is.
マイペース is used as a personality descriptor — a person who is "my pace" moves at their own rhythm regardless of what the group is doing. The English construction is impossible ("he is my pace"), which is a giveaway that this word was built here.
The double meaning is real and everybody knows it. In a culture where reading the atmosphere — 空気を読む (kuuki wo yomu) — is a core social skill, someone who does not is either enviably free or quietly a problem, and the same word covers both readings.
It is also becoming a compliment among younger people, in the same way "low maintenance" or "unbothered" has in English. Being unable to be rushed is increasingly aspirational in a country that has spent decades rushing.
This is the most Japanese word on this list, because it lets you deliver a criticism that the listener is free to hear as a compliment. No one is cornered. No one has to respond. If you want a single word that shows how this language handles conflict, it is not a swear word or an honorific — it is this one, said with a small laugh, meaning whatever the room needs it to mean.