For our xmas production, which finished last week, we had a full (25 people) orchestra, with flutes, clarinets, sax, trumpets, trombones, tenor horn, french horn, violins, double bass, and drum kit. I was sitting next to the sax player, and realized she was reading bass clef music.
I asked her what this was about and she said: "There's no Eb part. So I'm reading the bassoon part as though it's in treble clef and adding 3 sharps!"
What I found truly hilarious was that the tenor horn player had spent an entire weekend transposing all 100 pages of the score on Sibelius!

I didn't know that that worked for Eb instruments...

If you play Eb sax with Bb clarinet fingering lower register on Bb parts, that works too (except no one but me seems to be able to get their head round it!)

I've discovered that if I use flute fingerings on my clarinet in the lower octave, I can play the same pitch and my friends alto sax

Players of baritone horn, euphonium and tenor sax can read tenor clef as treble by adding two sharps. Brass band tenor trombone players sometimes learn treble clef, Bb transposing, first and can do the same. Orchestral trombone players learn tenor clef first and can do the reverse when they are given treble clef parts in the brass band.

I have a trombonist friend that seems to be able to read numerous keys by "imagining" them as "in another clef with a number of flats and sharps added". Completely baffling concept. When I play bass clef stuff, I actually have to work out the notes, so there's some lag, though I guess if I did more (or learnt to play a bass instrument) I'd get quicker.

Just don't ask me to play any C-clef stuff any time soon...

My daughter had to do this today playing Christmas Carols in a concert She was a bit suprised as it wasn't exactl;y expected.

I have to do the opposite when playing the bassoon along with my brother on the alto sax - play as if it's in bass clef, taking off 3 sharps (or adding 3 flats, or whatever). Just can't be bothered to transpose properly. But I play clarinet at church for the hymns, with a piano, another clarinet and a cornet (also Bb). Transposing major 2nds is actually quite easy. (Lots of practice, I suppose, and the pianist is crazy and plays everything stupidly fast.) My flautist friend (who's about the same standard as me) can't do it, though!