A stronger kind of squeeze applied to the exterior of a crisps packet, when you REALLY want someone to withdraw their hand out of it. Only works if packet belongs to you. Preceded by Gentle squeeze, and only used if it fails to achieve required effect.
Bing: (While making smalltalk) *Inserts hand into Bha's crisps packet*
Bha: (While listening or replying to smalltalk) *Performs Gentle squeeze)*
Bing: *Continues to fish for crisps in Bha's packet*
Bha: *Performs Strong squeeze*
Bing: *Withdraws hand*