If he has a wet dream in the wilderness, how can he do ghusl when his friends are present?
Question

                What is the ruling on one who has a wet dream when he is in the wilderness, in fair climatic conditions, and he does not do ghusl, because he feels embarrassed in front of his friends? How should he do ghusl in the wilderness? Should he take off all his clothes, because that is embarrassing and he is afraid someone might see him?.
Praise be to Allah.
    Firstly: 

    If a person becomes junub as a result of having a wet dream 
    or otherwise, then he must do ghusl. If he cannot find water, or he can find 
    it but he fears that he may be harmed by using it because it is very cold 
    and he cannot find any means of heating it, then he should do tayammum and 
    pray. As for failing to do ghusl and pray when one has become junub, out of 
    embarrassment or shyness, that is not permissible, and it is a grave wrong 
    action and is one of the causes of punishment in the grave. That has been 
    discussed previously in the answer to question no.
    65731. 

    Secondly: 

    There is no need to be naked when doing ghusl; rather what is 
    mustahabb for the one who is doing ghusl is to cover his ‘awrah with a 
    waist-wrapper and the like, even if he is doing ghusl on his own. 

    An-Nawawi (may Allah have mercy on him) said: In the previous 
    chapter we stated that it is permissible to uncover the ‘awrah in cases of 
    necessity when one is alone, such as when doing ghusl, when urinating and 
    when being intimate with one’s spouse, and the like. In all these cases it 
    is permissible to uncover when one is alone. But in the presence of other 
    people, it is haraam to uncover the ‘awrah in all cases. 

    The scholars said: Covering oneself with a waist wrapper or 
    the like when doing ghusl is preferable to uncovering oneself, although 
    uncovering oneself is permissible for as long as it is necessary, when doing 
    ghusl and otherwise; but doing that more than is necessary is haraam 
    according to the more correct opinion.

    End quote from Sharh Muslim, 4/32 

    Ahmad (544) narrated from al-Hasan (may Allah be pleased with 
    him) that he mentioned ‘Uthmaan (may Allah be pleased with him) and his 
    intense modesty, and he said: If he were in a room and the door was closed, 
    he would not take off his garment in order to pour water over himself; 
    modesty prevented him from standing up straight.

    Based on that, if a person is in the wilderness and wants to 
    do ghusl, he should cover the lower part of his body with a waist wrapper or 
    garment, and hide beneath a tree or far away from where people can see him, 
    or he should do ghusl sitting, so that his ‘awrah will not be visible; the 
    ‘awrah of a man is the area between the navel and the knee. 

    Thirdly: 

    If a person does not do ghusl in this case and does tayammum 
    instead, his tayammum is not valid and he has to repeat the prayers that he 
    offered before doing ghusl. 

    And Allah knows best.