Glaringly means in a way that is painfully easy to see — so clear that you almost cannot miss it. We use it most with words like obvious, clear, and wrong: a glaringly obvious mistake is one that jumps off the page. It belongs more to writing and careful speech than to soft chat; it has a slightly sharp, judging feel, as if the speaker is saying “come on, look.” Though actually, the older picture behind it is a hard bright light that makes you squint. People took that “too bright to ignore” feeling and laid it onto facts and errors. You will still hear glaring for harsh light, but glaringly in this use is about notice, not about lamps. It does not mean slowly, and it does not mean angrily, even though a glare can be an angry look — here the point is how easy the thing is to notice.