What would a straight Chinese man say to describe another man as "very gay"?
Arh hah, let me tell you the new generation expressions!

『同性恋者』is too formal to address a gay man. I would say it's equivalent to "homosexual".

The popular terms to the concept in Chinese have nothing to do with their original meanings, just as "gay" now has nothing to do with "joyous", but instead, they directly take after English counterparts.


他显然并非直男。
Obviously he is not a straight man.


Comment: Now in Chinese net community, the word 直男 is stigmatized by extreme feminists, referring to conservative, male-chauvinistic men. So it's now not a strict equivalence to "straight" in gender preference aspect.


他看起来给给的。
He looks like a gay.


Comment: Don't suspect!  It is actually a transliteration of "gay", and it IS the most common expression. And for this reason, often it's used unchanged as "gay".


他看起来gaygay的。
他一看就是弯的辣～


Comment: To avoid being seemingly harsh, often we use some tricks to soften the tone to show our innocence and acceptance. As in example, 辣 is a homophonic substitute to 啦, and a cursive ~ conveys (somehow) cute tone.


他明显就是基佬。


Comment: WARNING! Many homosexual people may feel offended by addressing them 『基佬』. It's derogatory. The etymology of 『基』meaning homosexual related is now hard to determine. Here are two explanations: 1. 基 in Cantonese is pronounced very similar to "gay". 2. In ancient Chinese, 㚻 （ji1）is the character for homosexual practice, which has evolved to 鸡, finally to 基. But whatsoever, 基佬 in Cantonese （as in Mandarin now）is derogatory. However, 基 used alone is not derogatory, as in 『腐眼看人基』.

活学活用，EXAMPLE（轻小说文风）：

我的新同桌似乎是个基佬。自上次座位轮换他与我同桌以后，我上课时常能感受到侧方的异样目光。原本我不是很在意，但偶然投以回视，发现他正奇异地注视着我，那是什么神情？稍有些怯退又探寻的眼神，像是由于实在太过喜欢（？）但又害怕主人发现而盯着鸟笼的橘猫所表露。四目相对，他疾速收回双眼，这次轮到我凝神注目，看他有何动作。果然，不到一分钟，一双黑眸又瞥到我这里，但发现我居然正在看，便泄气地折返。诶呀呀，这也太给了啦！我思忖着自己有什么优点呢？瘦高、匀称、四肢颀长，嗯唔，算是分明的五官吧！此后很久我都不再察觉他偷瞄了，突然稍有不习惯。课正讲到无聊的部分，我不禁端详起同桌来：嗯嗯，头发浓黑茂盛、粗硬，短茬勾勒出圆润的后脑，深颔，嘴唇饱满，隆准……还不错，我想着。至于眼睛嘛……我移动目光向眉眼看去，正接上他深邃的瞳仁——我大吃一惊：“你你你看我干嘛，好好上课啦！”他没有回应，只不过缓缓转动眼珠向我扫射，眉梢轻挑，下巴微抬——“啊，被我发现了～”，他一定是这样想的吧！我感觉皮肤有些干燥，摸一摸脸，居然滚烫！明明，明明是他先的，我有什么紧张的呢！“但他确实还挺好看的……”停停停停！这一句是从脑海哪个角落冒出来的？难不成我要给魂觉醒，从此被掰弯了？我十八年来都是钢铁大直男哎哎哎哎！“哪里有★那么多可爱的女同学，你看上哪一个了？”啊，不要再这样想了！正当脑内挣扎之时，我忽略了右方，浅浅的笑意。

Nah~ I used all four ways to express "gay". May this short paragraph help your own writing!