Get beside yourself
A modern phrase invented by a millennial of telling somebody to be humble and taking a crystal clear look at themselves before passing judgement and/or being critical towards others.
"Maybe you should sit back down and re-evaluate your thoughts, be humble... and get beside yourself."
You're getting beside yourself
My Grandma was Southern born and raised, so a lot of Southern Dialect , sayings and nuances were little lessons throughout my life. One of those sayings that I favored is " You're getting besides yourself"- My grandma would say this to me anytime she felt I was trying to "show off", "Act up" or get "too cutesy". It was a soft way of saying, "get back in line", or "get yourself together", "humbly thyself". It is usually used by someone elder or maternal/paternal, is helpful and surely is an expression of love!
You better stop misbehaving young lady, you're getting beside yourself...