How do you say I resent it to because think would understand having seen only once before in French?

Here are a few ways to translate "I resent it because I think you would understand having seen it only once before" into French, depending on the context and the desired level of formality:

Formal:

* Je le ressens d'autant plus que je pense que vous comprendriez, l'ayant vu seulement une fois auparavant. (This is a more literal translation, emphasizing the "resentment" aspect)

* Je suis d'autant plus contrarié(e) que je pense que vous comprendriez, l'ayant vu seulement une fois auparavant. (This uses "contrarié(e)," which translates to "upset" or "annoyed," and is less strong than "ressentir")

Informal:

* Ça me gonfle parce que je suis sûr(e) que tu comprendrais, l'ayant vu qu'une fois avant. ("Gonfler" is a colloquial expression meaning "to annoy")

* Je suis vraiment énervé(e) parce que je suis sûr(e) que tu comprendrais, vu que tu l'as vu qu'une fois avant. ("Énervé(e)" means "angry," but in this context, it can also convey a sense of frustration)

More idiomatic:

* Je suis vraiment vexé(e) parce que je pense que tu comprendrais, vu que tu l'as vu qu'une fois avant. ("Vexé(e)" means "upset" or "offended," and carries a connotation of feeling disrespected)

Remember:

* The choice of the verb ("ressentir," "contrarier," "gonfler," "énervé(e)," "vexé(e)") will influence the strength of the expression.

* You can also adjust the level of formality by choosing different words like "vous" (formal) or "tu" (informal).

* The phrase "l'ayant vu seulement une fois auparavant" can be shortened to "l'ayant vu qu'une fois" or "vu que tu l'as vu qu'une fois avant" for a more casual tone.

Ultimately, the best translation will depend on the specific situation and the intended meaning.