Around 350 points, with Quixotic on the top left corner, earning double triple words, a double letter on the X, and a 50 point bonus for using all my letters. It’s been downhill ever since then.
Online, I once played RELOADER (no blanks, IIRC), a triple-triple with the first E being the letter I built off of (from a very well-placed JUGGLE, so I completely understand why my opponent thought it was worth it).
I forget how many points, but you can calculate yourself.
I once made “QUALMIER” across two triple-word scores, along the bottom of the board, from center to right. That’s 10 + 1 + 1 + 1 + 6 (double letter) + 1 + 1 + 1 = 22 * 3 = 66 * 3 = 198 + 50 = 248. My sister protested that it’s not a word, but our dictionary showed “qualmy” so she had to accept that the comparative was real. My family still tries to work that word into conversation sometimes.
I’ve scored exactly 212 several times; QUITTERS was one and I forget the others, but nothing too exotic, on the trip-trip. Against me, the record was for OVERZEAL (300-odd) in the usual place.
About 10 years ago, I got 168 points in one play with QUIZZES using a blank for one of the Zs, Q on a double letter score, triple word score, 50 point bonus for using all 7 letters in the tray, and the S crossed with a previously played word to pluralize it.