To act like a right Hobnob in the tea, is to have a tantrum and deliberately sabotage something nice, either for yourself or someone else. Taken from the selfish nature of the hobnob biscuit, which presents itself as a tough 'come dunk me bro' biscuit, only to crumble when submerged. Similar to 'pissed on your chips'.

the thing that you don’t have when you’re phones percentage is over 20