does anyone play C instead of Bb in 1st position of trombone.?

Not sure what you mean. Which clef are you talking, and are you talking about using triggers, or note bending or what?

i think i know what you're on about - first position is a concert Bb only because of how i was taught i think of it as a C - am i right?

Of course. Brass band music sometimes has trombone notated as a Bb transposing instrument in treble clef. That way a player of euphonium or baritone horn can play from it without thinking about transposition and the right pitches will come out. When I played in a brass band, about 55 years ago, there was an army trained trombonist who used to coach the youngsters. He would ask us to play a note on our instrument, indicating it by its normal written pitch, and then say, "What's that for the band?". What he meant was, "What is that in concert pitch?" Every conductor needs to have these transpositions at his finger-tips, and it's very useful for composers too, though they don't have to think quite as fast, because they don't keep 80 expensive musicians waiting while they think about it.

I play treble clef, so yes 1st position is for me a C, although it sounds a Bb