How do you explain that someone takes all the credit ?

The situation is there is Mr A who does nothing at all, yet takes all the credit for everything.

Chub mue perb ชุบมือเปิบ

Chuy ogart ฉวยโอกาส

"credit", in this case, is "ความดีความชอบ" (kwam dee kwam chob)

I can't think of a particular word that concisely describes such a person, but you might say something like this:

เขาได้ความดีความชอบทั้งๆที่ไม่ได้ทำอะไรเลย

= He got all the credit even though he didn't do anything at all.

Hope that helps If it doesn't quite fit, try explaining the context it's meant to be in, maybe also the sentence you're thinking of.

I would call these type of people พวกชุบมือเปิบ

พวกชุบมือเปิบ puark chub mue perb

and describe the situation as a บุญหล่นทับ or ส้มหล่น

บุญหล่นทับ boon lon tub

สัมหล่น som lon

I would call these type of people พวกชุบมือเปิบ

พวกชุบมือเปิบ puark chub mue perb

This is what I've heard before for exactly such a person.