Yawning Face

The surrounding words help separate sleepiness from boredom. After a mention of an early start or poor sleep, it fits “I can barely stay awake.” Beside a complaint about waiting, it fits “this is dragging on.” As a reaction to a boast, it can dismiss what someone said as unimpressive.

A late-night message makes tiredness plausible, but the hour alone doesn't settle it. With no words or shared context, both tiredness and boredom remain possible. Between friends it can also be a tease; the emoji doesn't tell you how seriously to take it.

Is 🥱 rude?

It can be, when the yawn targets someone else's words. Yawning at a story or announcement can suggest it isn't worth your attention. The hand covering the mouth depicts a polite gesture, but it doesn't make a dismissive message polite.

If you mean physical tiredness, give it a few words: “barely slept 🥱” is clearer than the emoji alone. Likewise, receiving a lone 🥱 is a reason to check the context, not a reliable verdict on someone's feelings about you.