quote:under what circumstances would one use bheith
The verbal noun "bheith" is used when you use "to be" in English:
bheith ina fhear = to be a man, tú a bheith anseo = you to be here, bheith seafóideach = to be ridiculous, etc.
"Ag bheith" can't be correct, because bheith must not be lenited after ag (so it would be "ag beith"), but that isn't used.
(barring the usefulness of the adjective seafóideach instead of the noun seafóid, I would say that sentences like "being x" could be rendered so:
I'm ridiculous = Bím seafóideach
I'm being ridiculous = Tá mé seafóideach.
(Irish has a special tense where English must use constructions like "being")
Lars