I am not good enough to assess what is the right weight of lead needed by a buddy just before jumping. There are too many factors. With the same wetsuit, BCD (except the size), I need the same lead than my wife who is 15 cm shorter than me and 10 kg lighter. Without a pre-dive weight check, I can’t do it.
No, you can ask, well before it is time to jump. If the individual says "I don't know", that is a good sign you might have to watch for a Lawn Dart. If they say double your weight and they are similar in size, you can at least open the discussion. If the person has 5-6 lbs too much, it probably won't be terrible, but I have seen people being way, way off. In general, with an aluminum tank, 3 mm suit and "normal" body, somewhere around 12 lbs is reasonable. You start seeing 20 or more, you may be smart to ask some more questions.
Some people really do require more lead than seems necessary, but in general, if that is true for the individual, they probably know that and will be able to comment to that effect. Women generally are less dense than men and carry fat better, so they often use a little more than you might expect if you never paid attention in the past.
If you approach it somewhat as being curious, and you act like you are unsure how much lead to use "for this first dive", they might be more forthcoming in what they use.
You probably want to avoid a situation, which devolves into" "hey fat bastard, just how much lead do you have there". As long as the person knows how much they have and seem to be able to talk about it in some reasonable manner, you have done more than your part.