Boris has been thinking long and hard about the circumstances in which he would stay on and in which he would resign. Being found guilty of murder is almost certainly a resignation issue, as are any treason offences (high, medium or low).
Things that are not to be resigned over include fixed penalty notices, speeding fines, littering, sounding horn in a built up area after 10pm, shoplifting, breaches of the peace, pieces of the breeches, breaches of the ministerial code, mendacity, repetition, hesitation, repetition and deviation (up to a point).
The grey areas - might resign, might not - include the bodily harms (actual, grievous), assault (common, with a deadly weapon), bigamy, trigamy, failure to pay maintenance.
Finalising these lists is subject to further work with focus groups.