An exclamation used to express how exciting or overwhelming something is, literally to the point that it is making one's heart beat too quickly. It is almost often used sarcastically to imply that something is actually unremarkable, dull, or unpleasant; entailing the opposite effect.
Howard: I would have been able to go to the party with Kevin after work, but my hardass boss wants me to stay and finish my co-worker's paperwork for him. Be still my heart!
John: Jane just asked me out, be still my heart!
John: Jane just asked me out, be still my heart!
by TheGayAccount November 17, 2022