What if you stopped wearing masks everywhere you went and if people got on your case about it, you simply tell them that you've already had the vaccine and you're good to go.
The best part is, if they keep pressing, simply respond with "I thought the vaccine was supposed to end the pandemic? Are you saying it doesn't do anything to lessen the severity of the virus? If you're wearing your mask and I got my vaccine, everything should be ok". See their heads spin as the contradiction in the programming within their internal logic processor causes a kernel panic :)
Personally I cannot tell a lie so I would finesse it:
"The vaccine means I don't have to wear a mask" "After taking the vaccine you can expect to take off your mask" "Once you are immune, the mask is not required"
The above, in my book, arent lying but saying "I have taken the vaccine" is lying if you haven't. I might have told the odd lie when I was a child, but with a bit of language finesse you can learn to use ambiguity and let the listener jump to the conclusion you want. If they spot the evasion and ask for clarification: "You're obviously a smart cookie - what other discrepancies have you noticed lately?" and smile.