Выражение "быть не в своей тарелке" означает чувствовать себя неловко, неуютно, не комфортно.

to be in the wrong box

https://ru.wiktionary.org/wiki/%D0%BD%D0%B5_%D0%B2_%D1%81%D0%B2%D0%BE%D0%B5%D0%B9_%D1%82%D0%B0%D1%80%D0%B5%D0%BB%D0%BA%D0%B5 Note that in the first exapmle there (from Griboyedov) it likely (I don't remember the context) refers to condition/mood of a character, while in modern speech I hear it... Well, mood/feeling again, but the kind of it which can't be easily diagnosed by an observer:) And thus unlikely to appear in a such a categoric second person statement. Vague feeling of disomfort, sometimes, not necessary, the one associated with literal reading: like in company not much familiar to you. Or sometimes discomfort for an unknownt cause (of sosial, physical, nervous... any nature): целый день он чувствовал себя не в своей тарелке и не мог понять почему. Note also possible etymology below

To be not in it's right place.

out of place. it's like a fish out of water