When something is more almost than another something.
Oh well it's almost St-Patties Day, but it's almoster Friday!
Someone who wines and dines girls in the attempt of sleeping with them but frequently comes up short.-only to describe the events as an almost success.
Phil: hey how'd things go with christy last night?
Sean: I almost fucked her.
Phil: ahh you suck, youre such an almoster.