Yeah I definitely find this is true. For me its usually Js, Bs, Ds, Cs, but it also depends what vowel comes after the letter. For example 'jam', no worries, can say that all day long. But 'Jenny, could you pass the jam?' well im screwed...looks like plain toast for me. I good mechanism I've used is just to think of alternate ways to start the sentence as I'm better at not stuttering if im already speaking fairly fluently, like you its the start of the sentence that is my bane, especially being asked to repeat myself. I also think confidence is pretty important, if im nervous, ill stutter more. With regards to asking the girl out, if you seem nervous/stuttery then dont worry about it. If they're put off by your stutter then they obviously weren't the one anyways :)