Introduce yourself in your native slang

[ermitonto]

I never heard of someone with a Boston accent not pronouncing their "rs" at the beginning of the word.

A Bostonian would say "Let's go to the Boston Gahden."

But they would also say "Fuck Alex Rodriguez." They still say the R sound at beginning of words.

You would never hear "Fuck 'Andy Johnson" or "my cah is 'eally nice"

Yes, you are correct. Those dialects of English which don't pronounce all their R's only omit the R if the R doesn't come before a vowel sound (like it always does at the beginning of a word), so "law" and "lore" sound the same, as do "calmer" and "karma". And sometimes they'll reverse the process: since they can't tell the difference between "law" and "lore", some of them will insert an R-sound to either word if the next word starts in a vowel and say things like "lore and order" or "Chiner and Japan", which sound funny to those of us who pronounce an R every time we see one (and in the word "colonel" which should have an R but doesn't due to a freak linguistic accident).