Eight step Plan
1. Go ahead and make the purchase whatever it may be, Koni FSD's & Eibach's, new TV, trip away etc. etc.
2. Keep it quiet for as long as possible (this keeps ear ache down to a minimum)
3. As and when the new purchase is about to be delivered or you are about to go on that trip with the lads, start dropping subtle hints.
4. SWMBO finds out about said purchase/up coming trip
5. All hell breaks loose (be prepared for a rocky ride for up to a week)
6. SWMBO calms down (but has still not forgiven you so tread carefully)
7. After around two weeks everything is back to normal.
8. Start planning the next purchase/trip