I can't help noticing you skipped your part of that question Mycroft. Most creative thing you have ever done as revenge to Sherlock ?
When he was a child I emptied out his chemistry set and filled them up with items from the kitchen. I guaranteed that any experiment would led to some form of mess around explosion.
Eurus caught me doing it so I recruited her in finding items of the right consistency and management pulsating the colours.
When the inevitable explosion happened Eurus and I laughed for ten minutes.