Although this is a commonly used form in conversation, it is grammatically incorrect. The subject of your sentence is "Everyone" so the rest of the sentence behind "thinks" should begin with "he is" or "she is." It has become common to use "they" to avoid use of "he" to mean both men and women.

I think the second one is better

Conversationally either one is fine. And yes, I am a good kisser :-)

I think I can better understand it thanks to you, Kenny.

I cannot put it any better than Jean did ) . The other option is to use the " he or she" for the indefinite pronoun "everyone", but that sounds so clumsy that grammar is sacrificed for convenience ( so they rather use "their "and to hell with grammar). Or you can change the indefinite pronoun to definite > "everyone "becomes "all of us" to dodge this grammar trap . But, I read somewhere that in UK , this doesn't apply . Indefinite verb + singular tense + plural pronoun is ok , so yours are good there at least ) or conversationally fine anywhere ))