oof all the time. for me, these "nightmare words" are mostly those starting with a consonant (especially words starting with "p" and "c"). it gets so bad that i actively avoid saying any words which i know will make me block, substituting them for a synonym or quickly adding an extra syllable before it to make it easier to say (so for example "pizza" becomes "thepizza"). it doesn't always works, but it gets me by,,