After a co-worker thinks that Chandler is gay, he returns home/the girls apartment, where all 6 are hanging out. He appears stressed and confused and asks the others if they thought he was gay when they first met him. While all three girls agree that they actually DID think he was, the two guys both claimed that they did NOT think that.
During later episodes, showing flashbacks, Monica actually had a huge crush on him and became very upset when she overheard him laughing about it and making fun of her weight when she first met him. In my opinion this would indicate that she did NOT think that he was gay.
On the flip side, when they show Chandler interviewing Joey as a potential roommate, Joey states that he wanted it known the he was 'OK with the whole 'gay thing' ". Indicating, again in my opinion, that he actually DID think that Chandler was gay.
During later episodes, showing flashbacks, Monica actually had a huge crush on him and became very upset when she overheard him laughing about it and making fun of her weight when she first met him. In my opinion this would indicate that she did NOT think that he was gay.
On the flip side, when they show Chandler interviewing Joey as a potential roommate, Joey states that he wanted it known the he was 'OK with the whole 'gay thing' ". Indicating, again in my opinion, that he actually DID think that Chandler was gay.