Been in so many wouldn't be able to describe the detail of each one here, in one go.
Some have been judged by women measuring a bunch of guys, in an pre-organised way. Others have happened more spontaneously due to either drinking or just guys started to brag about dicks, yet again judged by women measuring.
Some have been almost instigated by women who have been aware of guys having large endowments and wanting to settle curiosity, sometimes if a guy has been bragging and annoying a girl, it's also happened in ways where women have asked to compare dicks to 'shut' them up.
They've taken place at clubs, pubs, parties and house parties in the above ways, but also there have been times in more 'relaxed' ways such as nude areas and gatherings where conversation on guys with large endowments have led to a compare as to which was the largest. Often when drink is involved as inhibitions are looser, but not always the case, just as much it's occurred where parties involved have been sober and ego has come to the fore. Sometimes bets have been wagered on them, in the form or money, partner 'swap', forfeit or just general pride.
They have also been times when it's a case of general acknowledgement more than a total compare. For example urinal situations where some guys have checked out the size of each other and a guy has either subtly or verbally acknowledged theirs were not as large.
I've not lost any to date, but had quite a bit of fun in them along the way and come across some rather well endowed individuals as a result.