cheesin: to grin insanely. Quite often after good news or a good getting into someone. If "pure" said in front of it, then a common Glaswegien saying emerges.
Not to be mistaken from the older sayin "cheesed off" used by middle aged people who still think that they are "hip"
I'm cheesin after last night Ay you're pure cheesin ya bam I'm cheesed of dudes 'coz I'm turning 50 tomorow