Dyeing armpit hair help request

Do any of y'all have any advice, tips and tricks on dyeing underarm hair? We are thinking of dyeing it for two different prides and just in general with some manic panic dye as that is apparently deemed to be safe for such things and we were wondering how to do it safely (moreso than just using a safe dye), how long it would last etc.

Any advice, tips and tricks or even links to exhaustive, easy to follow for beginners guides would be useful. Thanks!