That is largly an old wives tale...once the boys drop there is very little that one can do about pulling them back up.

Beisdes, as hard as some people kick---pulling them up insides would not really help you all that much.

And besides that, the process is not exactly like tighting a muscle--so its utilty is highly limited for how most attacks happen--by surprise and from ambush.

Good advice on the groin cup/mouth piece
I did battle with ignorance today.......and ignorance won. Huey.