Clinton Portis ain't just shutting the door on Landon Collins' wishes to wear Sean Taylor's old No. 21 jersey with the Redskins ... he's BOLTING it down, saying, "f**k no" he can't wear it!!
"F**k no," the ex-Washington running back says ... "I don’t ever want to see nobody else in it."
Of course, Landon just inked a MONSTER 6-year, $84 MILLION contract with the 'Skins ... and since he grew up idolizing Taylor -- some suggested he should wear the late safety's jersey number.
But that would rub at least one of Sean's old best friends the wrong way .