Top and bottom text in the correct Impact font, sized how you want, out as PNG. Free, no signup, and the file never leaves your device.
Exactly what you think.
Meme Generator is one of 22 free browser tools on IMGX Studio, filed under Make something. It runs entirely on your own device: the image is read in the browser, processed there, and never uploaded to a server, so there is nothing to delete afterwards and no account to create.
Open the tool, drop in an image, adjust the settings, and download the result. It works on desktop and mobile, there is no watermark, and there is no limit on how many times you use it.