From boak (Scotland/Northern Ireland) retching OR vomiting.
Note that vomiting is, duh, with vomiting (wet), and retching is without vomiting (dry), and the word boaking can mean either.
NOTE: For the non-"ing" form, boak, there is an explicit retching phrase: the dry boak (which is a noun).
Like many "ing" forms of verbs, boaking can be used as an adjective: the boaking bridesmaid, the boaking jerkwad who drank all my good scotch, etc.
"The ones not commenting on it were only refraining because they had their heads over the sides, boaking for all they were worth."
"I pull some Kleenex out from my jacket pocket. I always keep them handy for wiping purposes as you never know when some tight arsed cunt at HQ supplies will run short. I hand the boaking mess a couple. -- There you go mate."
Boaking - Causing An Accident To One's Self During Sexual Intercorse
"Hey Dude, i've been up all night with this Boaking accident", "Oh dude i don't wanna see that".